UC-NRLF 


GIFT   OF 
MICHAEL  REESE 


I 


POWDERED  COAL 
AS  A  FUEL 


BY 

C.  F.  HERINGTON 

•  i 

Mechanical  Engineer 


84    ILLUSTRATIONS 


NEW  YORK 

VAN  NOSTRAND  COMPANY 

25  PARK  PLACE 
1918 


Copyright,  1918 

BY 

D.  VAN  NOSTRAND  COMPANY 


PREFACE 


IN  placing  this  book  before  the  engineering  public,  the 
author,  who  obtained  much  of  the  information  herein  pre- 
sented while  employed  as  Assistant  Engineer  in  the  office 
of  the  New  York  Central  Railroad  Company,  wishes  to  give 
due  acknowledgment  for  valuable  aid  rendered  to  the  firms 
and  individuals  named  below: 

The  Fuller-Lehigh  Car  Wheel  and  The  Raymond  Bros.  Impact  Pul- 

Axle  Company  verizer  Company 

The  Bonnot  Company  The  American  Locomotive  Co. 

The  Ruggles-Coles  Company  The  Jeffrey  Mfg.  Company 

The  General  Electric  Company  The  Aero  Pulverizer  Company 

The  Webster  Mfg.  Company  The  Link  Belt  Company 

Prof.  R.  C.  Carpenter  Mr.  H.  Barnhurst 

Mr.  A.  A.  Holbeck  Mr.  James  Lord 

Mr.  J.  H.  Van  Buskirk 

Various  patents,  designs,  and  systems  are  here  described, 
but  the  author  wishes  to  emphasize  the  fact  that  compari- 
sons have  been  made  without  bias  and  claims  considered 
without  prejudice.  The  underlying  object  has  been  not 
to  advertise  the  advantages  of  any  one  system,  but  to  show 
the  merits  of  all. 

C.  F.  H. 

OCTOBER,  1917. 


376J32 


CONTENTS 


PAGE 

PREFACE v 

CHAPTER 

I.  INTRODUCTORY 1 

General  Operation  of  Plant — Comparison  of  Costs  with 
Oil  and  Gas 

II.  COALS  SUITABLE  FOR  POWDERING  . 8 

Experience  with  Various  Grades — Experiments — The 
Ash  Question 

III.  PREPARATION  OF  POWDERED  COAL 18 

Crushers — Dryers — Pulverizers — Air  Separation 

IV.  FEEDING  AND  BURNING  POWDERED  COAL 42 

Furnaces — Burners — Pneumatic  Distribution 

V.  POWDERED  COAL  IN  THE  CEMENT  INDUSTRY 62 

Edison  System — Kiln  Calculations — Utilization  of 
Waste  Heat 

VI.  APPLICATION  OF  POWDERED  COAL  TO  REVERBERATORY  FUR- 
NACES       78 

Canadian  Copper  Company — Washoe  Reduction  Works 
— Anaconda  Plant 

VII.  POWDERED  COAL  IN  METALLURGICAL  FURNACES 99 

General  Electric  Company — Furnace  Linings — American 
Locomotive  Company — Lebanon  Plant 

VIII.  POWDERED  COAL  UNDER  BOILERS 138 

General  Electric  Company— M.  K.  &  T.  R.R— Ameri- 
can Locomotive  Company 
vii 


viii  CONTENTS 

CHAPTER  PAGE 

IX.  POWDERED  COAL  FOR  LOCOMOTIVES 161 

Early  Use — Operation — Tests 

X.  EXPLOSIONS 178 

Storage  Difficulties 

BIBLIOGRAPHY .191 


LIST   OF   ILLUSTRATIONS 


FIG.  PAGE 

Frontispiece 

1.  Jeffrey  Single-roll  Crusher 18 

2.  S-A  Improved  Coal  Crusher 20 

3.  Fuller-Lehigh  Indirect-fired  Dryer 23 

4.  Ruggles-Coles  Dryer .  25 

5.  Fuller-Lehigh  Pulverizing  Mill 28 

6.  Fuller-Lehigh  Grinding  Ring 29 

7.  Raymond  Roller  Mill 31 

8.  Jeffrey  Swing-hammer  Pulverizer 35 

9.  Aero  Pulverizer '. 36 

10.  Bonnot  Pulverizer 38 

11.  Bonnot  Tube  Mill 40 

Pulverized  Coal  Plant 47 

12.  Whelpley  &  Storer  Apparatus 52 

13.  Whelpley  &  Storer  Apparatus 52 

14.  Crampton  Apparatus 55 

15.  Crampton  Apparatus . '. 55 

16.  Smith  Burner  and  Feeder 56 

17.  Smith  Burner  and  Feeder 56 

18.  Smith  Burner  and  Feeder 56 

19.  West  Feeder 57 

20.  West  Feeder 57 

21.  Holbeck  System,  Showing  Indicator  Dials 60 

22.  Rotary  Cement  Kiln 65 

23.  Injector  for  Cement  Kiln 66 

24.  Elongated  Flame  in  Cement  Kiln 67 

25.  Edison  System 69 

26.  Edison  System 69 

27.  Reverberatory  Furnace  Using  Powdered  Coal 86 

28.  Reverberatory  Furnace  Using  Powdered  Coal 87 

29.  Powdered  Coal  in  Open  Hearth  Furnace 100 

30.  Open  Hearth  Furnace  for  Powdered  Coal 106 

31.  Fuller  Pulverized  Coal  Plant 108 

32.  Fuller  Pulverized  Coal  Plant 108 

33.  Fuller  Pulverized  Coal  Plant 110 

ix 


X  LIST  OF  ILLUSTRATIONS 

FIQ.  PAGE 

34.  Mann  Burner 112 

35.  Mann  Burner 112 

36.  Mann  Burner 112 

37.  Fitting  for  Introducing  Primary  Air 115 

38.  Feeder  Box — Longitudinal  Section 115 

39.  Feeder  Box — Cross-section 115 

40.  Feeder  Box  Screw 115 

41.  General  Electric  Co.  Powdered  Coal  Furnace 118 

42.  General  Electric  Co.  Powdered  Coal  Furnace 118 

43.  General  Electric  Co.  Powdered  Coal  Furnace 119 

44.  General  Electric  Co.  Powdered  Coal  Furnace 119 

Ingot  Heating  Furnace  Using  Holbeck's  System  of  Pulverized 

Coal 123 

Plate-heating  Furnace  Arrangements 127 

Continuous  Billet  Heating  Furnace  Using  Holbeck  System 131 

.  Rivet  Heating  Furnaces  Using  Holbeck  System 135 

45.  Outline  of  Lebanon  Furnace 137 

46.  Plant  Using  Coarsely  Ground  Coal  under  Steam  Boiler 139 

47.  Heine  Boilers  Arranged  for  Pulverized  Coal 140 

48.  Heine  Boilers  Arranged  for  Pulverized  Coal. 140 

49.  Heine  Boilers  Arranged  for  Pulverized  Coal 140 

50.  Pinther  Apparatus 141 

51.  Schwartzkopf  Apparatus 142 

52.  Blake-Phipps  Apparatus 143 

53.  Bettington  Boiler 145 

54.  B.  &  W.  Boiler  for  Powdered  Coal. — General  Electric  Company.  147 

55.  Powdered  Coal  in  B.  &  W.  Boiler 148 

56.  Front  of  Boiler.— General  Electric  Co 149 

57.  Arrangement  of  Burners. — B.  &  W.  Boiler 150 

58.  Air  Currents  in  Boiler  Furnace 150 

59.  M.  K.  &  T.  R.  R.  Plant,  Parsons,  Kas.— Fuller  Engineering  Co. . .  155 

60.  M.  K.  &  T.  R.  R.  Plant,  Parsons,  Kas.— Fuller  Engineering  Co. . .  156 

61.  Boiler  Setting,  M.  K.  &  T.  R.  R 157 

62.  Locomotive  Equipped  for  Powdered  Coal 165 

63.  Powdered  Coal  Equipment  in  a  Steam  Locomotive 166 

64.  Single-Unit  Gravity  Milling  Plant,  Hudson  Coal  Co.     Capacity 

2  Tons  per  Hour 168 

65.  Double-Unit  Plant  and  Single-Bin  Locomotive  Coaling  Station. 

Capacity  8  Tons  per  Hour 169 

66.  Double-Unit  Plant  with  Triple-Bin  for  Loading  Locomotives. 

Capacity  16  Tons  per  Hour 170 

67.  Double  Burner  and  Firepan  Equipment  for  Locomotive,  Central 

Rwy.  of  Brazil 171 


LIST  OF  ILLUSTRATIONS  xi 

FIO.  PAGE 

68.  Double-Feed  Equipment  on  Locomotive  Fender,  Central  Rwy. 

of  Brazil 174 

69.  Double-Feeder  Equipment  for  Locomotive  Fender,  N.  Y.  C.  R.  R.  176 

70.  Triple  Burner  and  Firepan  Equipment  for  Locomotive,  N.  Y. 

C.  R.  R 179 

71.  Triple  Burner  and  Firepan  Equipment  for  Locomotive.     A.  T. 

&  S.  F.  Rwy 180 

72.  Triple  Feeder  Equipment  on  Locomotive  Fender.    A.   T.   & 

S.  F.  Rwy 181 

73.  Locomotive  Front  End  for  Powdered  Coal 182 

74.  Locomotive  Cab  Equipment  for  Powdered  Coal 183 

75.  Powdered  Coal  Equipment  for  Stirling  Boiler.     The  Hudson 

Coal  Co 185 

76.  Powdered  Coal  Equipment  for  O'Brien  Boiler.     M.  K.  &.  T.  Rwy.  187 

77.  Powdered  Coal  Equipment  for  Wickes  Boiler 189 


f 


POWDERED  COAL  AS  A  FUEL 


CHAPTER  I 
POWDERED  COAL— INTRODUCTORY 

COAL  is  the  staple  fuel  of  the  metal-working  industries 
because  of  its  wide  distribution  and  fairly  stable  price. 
It  may  be  secured  from  several  sources  by  almost  every  con- 
sumer and  the  coal  industry  is  so  widely  controlled  as  to 
lead,  generally,  to  favorable  prices. 

Powdered  coal  must  compete  with  raw  coal,  fuel  oil, 
and  industrial  gas.  The  elementary  factor  in  such  competi- 
tion is  the  B.t.u.  cost.  If  a  gallon  of  oil  containing  140,000 
B.t.u.  costs  five  cents,  then  the  B.t.u.  derived  when  one 
cent  is  spent  for  fuel  oil  will  be  28,000.  If  powdered  coal 
containing  14,000  B.t.u.  per  pound  can  be  purchased  for 
one-half  cent  per  pound  or  ten  dollars  a  ton,  then  there  are 
28,000  B.t.u.  obtained  for  each  cent  expended  to  buy  coal. 
The  two  fuels  are  then  on  a  parity  so  far  as  B.t.u.  cost 
goes,  but  any  final  analysis  must  consider  also  the  compara- 
tive efficiencies  in  the  furnace  of  the  two  fuels.  If  a  cent's 
worth  of  coal  will  go  farther;  that  is,  last  longer,  or  pro- 
duce more,  in  a  given  furnace  than  a  cent's  worth  of  oil 
(even  though  both  are  represented  by  the  same  number  of 
B.t.u.),  then  the  coal  is  to  be  preferred. 

Fuel  oil  fluctuates  sharply  in  price  and  tends  to  become 
more  expensive  as  demand  increases.  The  same  state- 
ment is  true  of  natural  gas.  It  is  not  true  to  anything  like 
the  same  extent  for  coal.  Raw  coal  can  not  be  compared 
with  powdered  coal  with  respect  to  efficiency  of  combustion. 
With  proper  appliances  and  methods,  the  last  produces  an 


2  POWDERED  COAL  AS  A  FUEL 

almost  smokeless  fire  with  a  steady,  intense  heat  and  maxi- 
mum furnace  temperature. 

It  is  true  that  the  number  of  powdered  coal  plants  is 
still  small.  Some  of  them  have  been  in  service  for  ten  to 
fifteen  years  and  these  have  fully  demonstrated  the  feasibility 
and  efficiency  of  a  powdered  coal  installation.  Fully  90 
per  cent  of  the  Portland  cement  made  in  the  United  States 
is  burned  in  kilns  in  which  powdered  coal  is  the  fuel.  The 
change  from  other  fuels  to  powdered  coal  does  not  involve 
expensive  furnace  reconstruction.  Any  furnace  adapted 
for  fuel  oil  or  gas  may  with  slight  changes  be  utilized  for 
powdered  coal. 

The  fuel  to  be  used  for  pulverizing  should  be  bituminous 
or  semi-bituminous,  either  the  slack  or  the  run-of-mme. 
Coals  rich  in  volatile  matter  are  to  be  preferred.  An  ad- 
vantage of  slack  over  run-of-mine  is  that  with  the  former 
no  preliminary  crushing  is  necessary.  The  following  anal- 
ysis represents  a  dried  coal  that  has  been  found  to  give  good 
results: 

Per  Cent 

Fixed  carbon 54.00 

Volatile  matter 32.75 

Ash 12.00 

Moisture 1 . 25 

v 
GENEKAL   OPERATION   OF  POWDERED   COAL  PLANT 

If  not  already  in  fine  particles,  the  coal  as  received  is 
crushed  so  as  to  pass  through  a  J-in.  ring.  It  is  then  dried 
in  a  direct-heat  contact  drier.  The  cost  of  the  drying  is 
appreciable,  but  this  operation  is  absolutely  necessary 
in  order  to  permit  of  gool  pulverizing.  Usually  the  per- 
centage of  moisture  is  reduced  to  about  1.0.  The  expendi- 
ture of  heat  for  the  drying  operation  is  not  a  net  loss  since 
no  fuel  of  any  kind  ever  burns  in  a  furnace  until  the  moisture 
contained  therein  has  been  evaporated. 

Following  the  drying,  the  coal  is  pulverized  in  some  one 
of  the  various  types  of  grinder  or  mill,  described  in  later 


POWDERED  COAL— INTRODUCTORY  3 

chapters.  It  is  made  so  fine  that  about  85  per  cent  will  pass 
through  a  200-mesh  screen  and  about  95  per  cent  through  a 
100-mesh  screen.  A  separating  device  is  usually  integral 
with  the  pulverizer.  This  carries  off  the  finer  particles 
while  returning  the  grosser  for  regrinding. 

The  finely  ground  coal  is  now  carried  to  bins  from  which 
it  is  fed  to  the  furnace  as  required.  The  furnace  construc- 
tion and  operation  must  be  such  that  the  lining  remains 
continuously  hot;  which  implies  a  steady,  uniform  feeding 
of  the  coal.  This  feeding  must  be  under  positive  control, 
along  with  which  must  go  a  positive  control  of  the  air  supply. 
The  fire  is  started  by  lighting  a  piece  of  oily  waste,  placing 
it  before  the  burner  and  turning  on  the  coal.  As  is  the  case 
with  fuel  oil,  the  combustion  is  not  very  efficient  until  after 
the  furnace  is  warmed  up. 

COMPARISON   OF  COSTS,   FUEL  OIL,   WATER  GAS  AND   PULVER- 
IZED  COAL 

The  following  approximate  figures  are  intended  to  show 
under  the  assumed  conditions  the  relative  costs  for  instal- 
lation and  operation  of  the  three  kinds  of  equipment  named. 
It  is  assumed  that  there  are  45  furnaces  and  that  the  heat 
consumption  is  9,100,000,000  B.t.u.  per  month. 

The  assumed  heat  consumption  is  equivalent  to  65,000 
gallons  of  oil  of  140,000  B.t.u.  per  gallon  or  to  650,000 
pounds  of  coal  at  14,000  B.t.u.  per  pound.  For  the  gas 
plant  it  will  be  assumed  that  each  cubic  foot  of  gas  contains 
474  B.t.u.  and  that  20  cu.ft.  of  gas  are  produced  per  pound 
of  coal.  Then  the  coal  consumption  per  month  for  making 
the  gas  is  9,1 00,000,00  -f-  (20x474)  =960,000  Ib. 

This  corresponds  with  a  gas-making  efficiency  of  0.68, 
which  of  course  cannot  be  realized  when  only  water  gas  is 
made.  If,  however,  both  producer  gas  and  water  gas  are 
furnished  from  the  same  plant,  the  combined  efficiency 
may  be  as  high  as  that  assumed.  The  producer  gas  will 
then  be  used  for  low-temperature  work  and  the  water  gas 
in  furnaces  requiring  high  temperature. 


4  POWDERED  COAL  AS  A  FUEL 

1.  Fuel  Oil,  First  Cost  of  Plant 

Three  10,000-gal.  storage  tanks  at  $850 $2,550 . 00 

Unloading,  excavation,  and  setting  tanks 900 . 00 

Two  auxiliary  pressure  tanks  in  place 2,000 . 00 

One  circulating  pump  and  motor 150 . 00 

Piping,  fittings  and  valves 5,000 . 00 

Steam  and  air  connections  to  tanks 1,500 . 00 

Connections  to  furnaces,  45  at  $50 2,250.00 

Standpipes  for  tank  cars 150 . 00 

Pump  and  pump  house 500 . 00 

Blowers,  motor  and  blast  connections 5,000 . 00 


Total $20,000.00 

Contractor's  profit,  15  per  cent 3,000.00 


$23,000.00 
Engineering  and  contingencies — 10  per  cent 2,300.00 


$25,300.00 


2.  Water  Gas,  First  Cost  of  Plant 


Gas  plant  machinery  erected  in  place $45,000.00 

Building,  complete  with  foundations 20,000 . 00 

Coal  trestle,  hoppers  with  siding 6,500 . 00 

Gas  piping,  meters,  valves,  water  piping 12,500.00 

Changes  in  furnaces 4,000.00 


Total $88,000.00 

Contractor's  profit,  15  per  cent 13,000.00 


$101,000.00 
Engineering  and  contingencies,  10  per  cent 10,000 . 00 


$111,000.00 

With  regard  to  the  powdered  coal  plant,  two  types  of 
apparatus  will  be  considered.  The  first  is  that  in  which 
screw  conveyor  apparatus  is  used  for  distributing  the  coal, 
with  individual  bins,  controls  and  feeders  at  each  furnace. 
Another  type  of  plant  (see  Chapter  IV)  is  that  hi  which  the 
coal  dust  is  carried  to  the  various  furnaces  by  means  of  low- 


POWDERED  COAL— INTRODUCTORY  5 

3.  Powdered  Coal,  Screw  Conveyor  Plant,  First  Cost 

Pulverizing  machinery $12,000 . 00 

Buildings  and  foundations 6,000 . 00 

Machinery  foundations 2,000 . 00 

Coal  trestle  and  track  siding 6,500 . 00 

Conveyor  system  to  the  furnaces 11,500.00 

Walkways  and  conveyor  supports 6,000 . 00 

Motors  and  wiring  for  conveyors 8,000 . 00 

Burners  and  controllers  for  45  furnaces  at  $250 11,250.00 

Furnace  changes,  stacks 4,250 . 00 

Furnace  bins,  45  at  $100 4,500.00 

Hoods  and  exhaust  system  complete 6,000 . 00 

Stack  thimbles  through  roof 1,000 . 00 


Total $79,000.00 

Contractor's  profit,  15  per  cent 12,000.00 


$91,000.00 
Engineering  and  contingencies,  10  per  cent 9,000 . 00 


$100,000.00 

4.  Air  Distributing  System,  Powdered  Coal,  First  Cost 

Pulverizing  Machinery $12,000.00 

Buildings  and  foundations 6,000 . 00 

Machinery  foundations 2,000 . 00 

Coal  trestle,  etc 6,500.00 

Spiral  riveted  pipe,  fittings  and  valves 8,500 . 00 

Furnace  changes 2,500.00 

Blowers,  motors  and  wiring 8,000 . 00 

Hoods  and  exhaust  system  complete 6,000 . 00 


Total $51,500.00 

Contractor's  profit,  15  per  cent 7,725.00 


$59,225.00 
Engineering  and  contingencies,  10  per  cent 5,925 . 00 


$65,150.00 

pressure  air  which  conveys  it  in  suspension  from  a  central 
storage  bin  (Holbeck  system). 


6  POWDERED  COAL  AS  A  FUEL 

Against  these  installation  costs  for  the  four  types  of  plant, 
we  now  tabulate  the  annual  operating  costs,  including  fixed 
or  overhead  charges : 

Operating  Cost  of  Fuel  Oil  Plant 

Fixed  Charges: 

Interest,  5  per  cent  of  $25,300 $1,265 . 00 

Depreciation,  10  per  cent 2,530 .00 

Taxes  and  insurance,  1  per  cent 253 . 00     $4,048 . 00 


Operation: 

Oil,  780,000  gal.  at  4.6  cents  per  gallon $35,880 . 00 

Labor,  two  men .' 2,000.00 

Electrical  current,  air  and  steam 720 . 00 

Repairs,  2  per  cent  of  the  cost 500 . 00  $39,100 . 00 


$43,148.00 

Operating  Cost  of  Water  Gas  Plant 

Fixed  Charges: 

Interest  at  5  per  cent  of  $1 1 1 ,000 $5,550 . 00 

Depreciation  at  10  per  cent 11,100 . 00 

Taxes  and  insurance,  1  per  cent 1,100.00   $17,750.00 


Operation: 

Coal,  5760  tons  at  $2.50 $14,400.00 

Labor,  1  operator  and  two  assistants 2,800 . 00 

Unloading  coal  at  $1.50  per  car 200 . 00 

Cleaning  generators 200 . 00 

Water 200.00 

Steam 200.00 

Repairs,  2  per  cent,  of  $111,000 2,200.00   $20,200.00 


$37,950.00 

Operating  Cost  of  Powdered  Coal  Plant  with  Screw  Conveyors 

Fixed  Charges: 

Interest,  5  per  cent,  of  $100,000 $5,000.00 

Depreciation,  10  per  cent 10,000.00 

Taxes  and  insurance,  1  per  cent 1,000.00  $16,000.00 


POWDERED  COAI^-INTRODUCTORY  7 

Operation: 

Coal,  3900  tons  at  $2.50 $9,750.00 

Labor,  1  operator  and  two  assistants 2,800 . 00 

Unloading  coal  at  $1.50  per  car 100 .00 

Electrical  current  for  motors 3,000 . 00 

Repairs,  2  per  cent  of  cost 2,000 . 00   $17,650 . 00 

$33,650.00 

Operating  Cost  of  Powdered  Coal  Plant  with  Pneumatic  Distributing  System 

Fixed  Charges: 

Interest  at  5  per  cent  of  $65,150 $3,257.50 

Depreciation  at  10  per  cent 6,515 .00 

Taxes  and  insurance 651 .00   $10,423.50 

Operation: 

Coal,  3900  tons  at  $2.50 $9,750.00 

Labor,  1  operator  and  two  assistants 2,800 . 00 

Unloading  coal  at  $1.50  per  car 100.00 

Electrical  current  for  motors 1,500.00 

Repairs,  2  per  cent  of  cost 1,140.00   $15,290.00 


$25,713.50 


SUMMARY 


First  Cost. 


Yearly  Operation. 


Fuel  oil  plant 

Water  gas  plant 

Powdered  coal  plant  (screw  conveyor).. 
Powdered  coal  plant  (pneumatic) 


$25,300.00 

111,000.00 

100,000.00 

65,150.00 


$43,148.00 
37,950.00 
33,650.00 
25,713.50 


More  briefly  still,  we  have  the  following: 


Operating  Cost 

per  Ton  of  Coal 

Burned. 


B.t.u.  Delivered  to 
Furnace  per  1  Cent 
of  Operating  Cost. 


Fuel  oil 

Water  gas 

Powdered  coal  (screw  conveyor). 
Powdered  coal  (pneumatic) 


$6.60 
8.65 
6.59 


25,300 
28,700 
32,500 

42,488 


CHAPTER  II 
COALS  SUITABLE  FOR  POWDERING 

POWDERED  coal  weighs  38  to  45  Ib.  per  cubic  foot, 
although  the  solid  particles  have  a  specific  gravity  between 
1.3  and  1.35.  The  free  surface  of  a  pile  at  rest  makes  an 
angle  of  34  to  38  degrees  with  the  vertical,  if  dry.  These 
properties  do  not  vary  much  with  the  grade  of  coal. 

EXPERIENCE  WITH  VARIOUS  GRADES  OF  COAL 

The  impression  has  prevailed  until  recently  that  only 
bituminous  coals  were  suitable  for  powdering. 

Bituminous,  or  soft  coal,  differs  from  anthracite  hi  its 
greater  proportion  of  volatile  content.  The  greater  the 
percentage  of  volatile  constituents  in  coal,  the  more  readily 
will  it  deflagrate.  These  volatile  gases  distill  from  the  fuel 
and  ignite  at  a  temperature  much  lower  than  that  required 
for  carbon  itself.  To  burn  them  requires  a  greater  relative 
supply  of  oxygen  than  that  necessary  for  carbon.  Their 
average  heat  value  is  nearly  50  per  cent  greater  than  that  of 
carbon. 

The  fuels  available  for  burning  in  Portland  cement  kilns 
may  have  a  wide  range  of  quality.  The  best  bituminous 
coals  are  preferable,  but  those  of  poor  quality  are  occasion- 
ally found  in  successful  use.  The  fuels  used  in  the  Eastern 
portions  of  the  country  are  generally  obtained  from  the  soft 
coal  mines  of  Pennsylvania  and  Maryland,  Virginia  and 
West  Virginia.  The  coals  employed  in  mills  in  the  West 
are  those  most  accessible  from  the  plant  and  cheapest  in 
price  on  the  heat  unit  basis. 

The  effort  to  use  low-grade  coal  has  been  at  once  one  of 
the  most  attractive  and  elusive  features  of  powdered  coal 

8 


COALS  SUITABLE  FOR  POWDERING  9 

firing.  Unsuitable  coal,  while  not  always  the  ultimate  cause 
of  failure,  has  often  been  the  immediate  cause  for  the  dis- 
continuance of  experiments.  While  it  is  possible  to  burn 
inferior  grades  of  coal  in  powdered  form,  there  are  often  so 
many  complications  introduced  as  to  overcome  any  economy. 
The  idea  of  using  up  the  extensive  anthracite  culm  piles 
may  have  to  be  abandoned.  The  particular  difficulty  with 
low-grade  coals  is  in  the  disposal  of  the  slag.  Average  slag 
moves  very  sluggishly  at  a  temperature  of  2500°  F.,  and  prac- 
tically all  slag  solidifies  at  1800°  or  above. 

As  a  single  example  of  the  effect  of  low-grade  coal,  Mr. 
W.  A.  Evans,  in  a  discussion  before  the  Western  Engineers' 
Society,  quotes  his  experience  with  a  malleable  iron  anneal- 
ing furnace.  "  Coal  containing  about  4  per  cent  of  ash 
was  being  used  with  very  satisfactory  results.  Exact 
control  of  the  heat  was  possible  throughout  the  annealing 
process.  A  very  small  amount  of  slag  was  deposited  in  the 
combustion  chamber  on  a  bed  of  cinders,  and  this  was  easily 
removed  every  twenty-four  hours.  One  of  the  officers  of 
the  company  compared  the  appearance  of  the  fine  powder 
with  that  from  a  cheap  slack  coal  that  could  be  bought 
for  about  half  what  the  good  coal  was  costing,  and  he  insisted 
upon  the  use  of  the  cheaper  coal.  It  did  not  take  long  to 
demonstrate  the  unavailability  of  the  substitute.  Slag 
deposited  rapidly  in  the  combustion  chamber  and  frequent 
opening  of  the  furnace  front  was  made  necessary  in  the  effort 
to  remove  it.  The  result  was  that  the  furnace  would  cool 
down.  The  saving  in  cost  of  fuel  was  soon  overcome  by 
complications  and  ruined  castings. " 

It  is  desirable  to  use  the  very  best  coal  obtainable,  when 
working  out  a  new  problem.  The  trial  of  cheaper  coal  can 
be  undertaken  when  other  details  have  been  perfected. 

EXPERIMENTS 

In  the  Engineering  and  Mining  Journal  of  1876,  Chief 
Engineer  B.  F.  Isherwood,  U.S.N.,  described  a  test  made  by 
naval  engineers  under  his  direction  in  1867  and  1868  at 


10  POWDERED  COAL  AS  A  FUEL 

South  Boston,  Mass.,  with  both  anthracite  and  semi- 
bituminous  coals,  in  commercial  and  powdered  forms.  The 
highest  rate  of  combustion  attained  was  13.8  Ib.  per  square 
foot  of  grate  per  hour  for  the  anthracite  and  14.9  Ib.  for  the 
bituminous,  referring  all  coal,  powdered  as  well  as  solid, 
to  the  grate  area.  Mr.  Isherwood's  conclusions  were  that, 
including  the  cost  of  pulverizing,  the  anthracite  did  a  great 
deal  better  and  the  semi-bituminous  a  little  better,  when 
burned  upon  the  grate  in  the  ordinary  way,  than  when  burned 
in  the  powdered  condition. 

The  powdered  coal  used  under  a  Bettingdon  boiler  which 
gave  an  efficiency,  under  test,  of  82.6  per  cent,  contained 
2.15  per  cent  of  moisture,  22.8  per  cent  of  volatile  matter, 
57.55  per  cent  of  fixed  carbon  and  17.5  per  cent  of  ash.  A 
number  of  these  boilers  (see  Chapter  VIII)  are  in  use  in 
South  Africa,  Great  Britain  and  Canada. 

For  metallurgical  furnaces,  the  practice  of  the  American 
Iron  and  Steel  Co.  of  Lebanon,  Penn.,  indicates  that  the 
volatile  content  should  be  not  less  than  30  per  cent.  A 
typical  coal  used  by  them  analyzed  1.12  per  cent  moisture, 
33.2  per  cent  volatile,  56.07  per  cent  fixed  carbon  and  9.61 
per  cent  ash.  The  American  Locomotive  Co.,  at  Schenec- 
tady,  N.  Y.,  uses  in  its  drop  forge  furnaces  a  coal  high  in 
volatile  matter,  low  in  ash,  and  dried  until  it  contains 
not  over  J  of  1  per  cent  of  moisture.  In  a  reverberatory 
furnace,  the  Canadian  Copper  Co.  employs  a  good  quality 
of  slack.  Analysis  of  one  lot  showed:  volatile  matter, 
34.70;  fixed  carbon,  55.40;  ash,  9.45;  sulphur,  1.30;  mois- 
ture, 4.31  per  cent.  This  coal  has  a  thermal  value  of  about 
13,500  B.t.u.  per  pound. 

One  of  the  most  severe  tests  yet  made  was  with  a  semi- 
bituminous  coal  from  Brazil,  analyzing  as  pulverized: 

Per  Cent. 

Moisture from    2-  8 

Volatile from  14^28 

Fixed  carbon from  58-34 

Ash..  .  from  26-30 


COALS  SUITABLE  FOR  POWDERING 


11 


The  sulphur  averaged  from  3  per  cent  to  9  per  cent  and 
the  B.t.u.  from  10,900  to  8,800.  No  difficulty  whatever 
was  experienced,  according  to  Mr.  J.  E.  Muhlfeld,  in  main- 
taining maximum  boiler  pressure  when  working  a  loco- 
motive with  this  fuel  under  the  most  severe  operating 
conditions.  The  ash  and  sulphur  contents  in  this  instance 
are  strikingly  abnormal  and  adverse  to  good  operation.  A 
more  usual  coal  for  locomotive  practice  is  mentioned  by  Mr. 
Muhlfeld  as  having  been  employed  on  an  Atlantic  type 
passenger  locomotive.  This  was  a  Kentucky  unwashed 
screenings  testing  2.46  per  cent  moisture,  36.00  per  cent 
volatile,  54.00  per  cent  fixed  carbon,  0.78  per  cent  sulphur 
and  7.94  per  cent  ash.  It  contained  13,964  B.t.u.  per  pound. 

In  Muhlf eld's  experiments  on  locomotives,  described 
in  the  Journal  of  the  American  Society  of  Mechanical 
Engineers  for  December,  1916,  mixtures  ranging  down 
from  75  per  cent  run-of-mine  bituminous  and  25  per  cent 
anthracite  birdseye  (over  T&  in.  and  through  A  in.)  to 
40  per  cent  of  the  former  with  60  per  cent  of  anthracite 
culm,  were  burned  with  equally  satisfactory  results.  The 
average  composition  of  the  coals  referred  to  is  shown  in 
the  following  table: 


Item. 

PULVERIZED. 

Bituminous 
Run-of-Mine. 

Anthracite. 

Birdseye. 

Culm. 

Moisture  per  cent      

0.50 
29.50 
60.00 
10.00 
1.50 
13,750 
86.00 

0.50 
7.50 
77.00 
15.00 
1.00 
12,750 
86.00 

1.00 
6.00 
71.00 
22.00 
2.50 
11,250 
86.00 

Volatile  per  cent            

Fixed  carbon  per  cent                .... 

Ash  per  cent 

Sulphur,  per  cent  

B  t  u  per  pound         

Fineness,  per  cent  through  200-mesh  . 

Satisfactory  results  are  also  reported  from  powdered 
lignite   having    an   analysis    of:    moisture,    1.8   per  cent; 


12 


POWDERED  COAL  AS  A  FUEL 


volatile,  47.0  per  cent;  fixed  carbon,  41.0  per  cent;  sul- 
phur, 0.75  per  cent;  ash,  9.5  per  cent;  with  a  heat  value  of 
10,900  B.t.u.  per  Ib. 

Mr.  Muhlfeld  claims  that  the  use  of  powdered  anthra- 
cite culm  will  double  the  steam-generating  capacity  of 
stationary  boilers  now  burning  birdseye  anthracite,  hand- 
fired  on  grates;  and  at  the  same  time  eliminate  fire  cleaning, 
greatly  decrease  the  amount  of  ash  to  be  handled,  and 
reduce  the  boiler-plant-labor  cost  about  40  per  cent.  He  has 
employed  birdseye  containing  7  to  9  per  cent  volatile  and 
19  to  22  per  cent  ash,  and  culm  containing  6  to  10  per  cent 
volatile  and  22  to  46  per  cent  ash,  in  tests  on  a  463  horse- 
power Stirling  water-tube  boiler,  with  the  following  results: 


Test  No. 

1 

2 

3 

4 

5 

6 

7 

Duration,  hours  
Horsepower  rating 

72 
463 

336 
463 

24 
463 

48 
463 

120 
463 

240 
463 

24 
463 

Horsepower  developed,  % 
Fuel: 
Kind  

133 

Anth. 
B'eye 

135 
Anth. 
B'eye 

147 
Anth. 
B'eye 

178 
Anth. 
B'eye 

112 
Anth. 
Culm 

118 
Anth. 
Culm 

124 
Anth. 
Culm 

Dryness,  per  cent  
Fineness,       per       cent 
through  200-mesh  .  .  . 
Evaporation,  from  and 
at  212°  F.,  Ib 

0.65 
86.0 

8  7 

0.65 
86.0 
8  9 

0.65 
85.0 
9  6 

0.65 
86.0 
9  8 

0.8 
88.0 

7  8 

0.8 
86.0 
8  1 

0.8 
88.0 
8  5 

CO2,  average  per  cent  .  . 
Vacuum    in    breeching 
uptake,  in.  of  water.  . 
Vacuum  in  combustion 
chamber,  in.  of  water 
Boiler  pressure,  average 
Ib  

16.6 
0.25 
0.16 
140 

16.3 
0.23 
0.14 
142 

15.9 
0.22 
0.13 
141 

16.6 
0.23 
0.16 
140 

1.62 
0.27 
0.17 
143 

16.5 
0.28 
0.19 
144 

16.7 
0.27 
0.15 
145 

Flue-gas  temperature, 
deg.  F.,  average.    .  . 

518 

525 

496 

603 

475 

580 

576 

SUMMARY 


Most  of  the  experience  hitherto  obtained  has  been  on  high 
grade,  highly  volatile,  soft  coals,  and  efforts  to  burn  inferior 
grades  have  often  led  to  disappointment.  It  is  in  recent 


COALS  SUITABLE  FOR  POWDERING  13 

practice,  and  in  the  hand  of  only  a  few  investigators,  that 
good  results  have  been  obtained  from  inferior  soft  coals  and 
from  anthracite.  All  of  the  most  recent  developments  for 
steam  generation  have  been  made  with  anthracite  culm, 
at  one  time  definitely  abandoned  as  a  suitable  fuel  for 
powdering.  Powdered  coal,  like  ordinary  commercial  coal, 
should  be  practically  free  from  sulphur,  for  all  but  the  most 
exceptional  applications. 

THE   ASH   QUESTION 

The  presence  of  inert  impurities  in  the  fuel  has  not 
much  effect.  Only  combustibles  will  burn;  the  combus- 
tibles, if  inert,  do  not  necessarily  affect  the  operation  of  the 
furnace.  Their  effect  is  in  the  reduced  amount  of  useful 
work  obtained  from  a  dollar's  worth  of  fuel.  Coal  has  been 
burned  which  contained  up  to  52  per  cent  of  ash.  Good 
performance  depends  not  so  much  on  the  per  cent  of  ash 
or  the  heat  value  of  the  fuel  as  upon  dryness,  fine  grinding, 
a  hot  fire  box  and  proper  air  supply.  One  authority  goes 
even  so  far  as  to  say  that  any  solid  fuel  that,  in  a  dry  pul- 
verized form,  has  two-thirds  of  its  content  combustible,  is 
suitable  for  steam-generating  purposes.  "  Domestic  and 
steam  sizes  and  qualities  of  anthracite,  bituminous,  and  semi- 
bituminous  coals,  and  lignite  and  peat,  as  well  as  the  inferior 
grades  such  as  anthracite  culm,  dust  and  slush,  and  bitu- 
minous and  lignite  slack,  screenings  and  dust,  are  all  suitable 
for  burning  in  pulverized  form." 

But  while  the  absolute  amount  of  ash  in  coal  may  have 
only  minor  influence  on  its  suitability  for  use  when  pow- 
dered, the  quality  of  the  ash  is  all-important. 

With  the  ordinary  method  of  burning  coal  under  a  steam 
boiler,  the  grate  (with  its  bed  of  solid  incandescent  fuel  more 
or  less  encumbered  with  ash  and  clinker)  offers  a  con- 
siderable, a  varying  and  an  irregularly  distributed  resist- 
ance to  the  passage  of  air,  rejects  the  incombustible  residuum 
with  some  difficulty  and  allows  some  of  the  unburned  fuel 
to  sift  to  the  ashpit  or  to  be  fused  in  with  the  clinker.  With 


14  POWDERED  COAL  AS  A  FUEL 

powdered  coal,  burned  in  suspension,  many  of  these  dif- 
ficulties disappear.  There  still  remains,  however,  the  dif- 
ficulty of  getting  rid  of  the  incombustible.  With  10  per 
cent  of  ash  there  will  be  200  Ib.  of  refuse  to  be  disposed  of, 
for  each  ton  of  coal  burned.  If  this  ash  is  kept  in  a  pul- 
verized form  it  is  carried  into  the  back  connection,  the  tubes 
and  stack,  and  scattered  about  the  neighborhood.  If  it 
is  fused,  an  even  more  serious  difficulty  may  arise.  The 
clinker  then  attaches  itself  to  the  surface  of  the  furnace  and 
welds  itself  into  large  masses.  This  may  occasion  damage 
to  the  brickwork  when  the  clinker  is  removed  and  necessi- 
tates comparatively  frequent  lay-offs  for  cleaning.  In  one 
instance,  the  molten  slag  formed  in  ridges  and  sheets  upon 
the  sides  and  in  stalactites  upon  the  roof  of  the  furnace, 
while  the  floor  was  covered  with  a  plastic  mass,  which  cooled 
when  the  door  was  opened  for  its  removal,  and  could  scarcely 
be  withdrawn  without  material  damage  to  the  furnace. 

According  to  Muhlfeld,  clinker  is  of  two  kinds:  "  hard  " 
and  "  soft."  "  Hard  clinker  "  is  formed  by  the  direct  melt- 
ing of  some  of  the  ash  content.  It  hardens  as  it  forms  and 
usually  gives  but  little  trouble.  "  Soft  clinker  "  is  formed  by 
the  slagging  of  the  ash  and  is  either  pasty  or  fluid  and  steadily 
grows  in  size.  "  Honeycomb  "  or  "  flue-sheet  clinker  " 
is  formed  by  the  condensation  or  coking  of  tarry  matter  or 
vapor  as  it  strikes  against  the  fire-box  sheets,  and  results 
in  the  accumulation  of  a  relatively  soft,  light,  ashy  substance 
that  grows  or  spreads  over  certain  of  the  refractory  or 
metal  parts  of  the  furnace. 

A  common  source  of  trouble  is  the  ferric  sulphide  (iron 
pyrites,  FeS2)  in  the  ash.  This  is  reduced  to  ferric  sulphide 
(FeS)  in  the  furnace.  The  latter  substance  melts  at  about 
2300°  F.  and  forms  a  pasty  mass.  If  subjected  to  high 
heat  and  an  excess  of  ah-,  it  forms  Fe20s,  ferric  oxide,  which 
combines  with  the  silica  present  in  the  ash  to  form  a  rela- 
tively harmless  infusible  clinker.  If  the  supply  of  oxygen 
is  insufficient,  on  the  other  hand,  the  ferric  sulphide  becomes 
ferrous  oxide,  FeO,  which  when  combined  with  silica  pro- 


COALS  SUITABLE  FOR  POWDERING 


15 


duces  the  troublesome  honeycomb.  Proper  adjustment  of 
combustion  conditions  to  suit  the  fuel  used  will  therefore 
help  to  mitigate  clinker  difficulties.  Generally  speaking, 
silica,  alumina  and  magnesium  decrease  the  fusibility  of 
ash;  while  iron,  lime,  potassium  and  sodium  tend  to 
increase  its  fusibility. 

The  ash  question  is  usually  less  serious  in  metallur- 
gical applications.  At  the  furnace  of  the  Canadian  Copper 
Co.,  referred  to  hi  Chapter  VI,  the  ash  from  the  coal  causes 
very  little  trouble  in  operation.  A  small  amount  settles 
on  the  slag,  but  as  the  ash  contains  considerable  amounts 
of  iron,  this  is  not  an  undesirable  feature.  A  small  quantity 
also  settles  in  the  flue  and  a  few  hundred  pounds  may  stick 
around  the  throat.  Where  exposed  to  high  heat,  the  ash 
forms  a  very  light  pumice-like  fragile  mass.  The  throat 
is  cleaned  out  daily  by  opening  the  door  under  the  flue. 
During  the  cleaning  the  firing  is  maintained  as  usual. 

The  possible  influence  of  coal  composition  on  the  analysis 
of  furnace  product  is  suggested  in  the  following  table,  which 
compares  results  obtained  in  the  same  furnace  with  fuel  oil 
and  powdered  coal : 


Analysis  of  Slag. 

Per  Cent. 

Oil. 

Coal. 

Si02     

16.0 
22.0 
7.4 
1.7 

0.025-0.035 
1.0-1.15 

16.5 
18.2 
6.7 
1.9 

0.035-0.04 

FeO       .           

MnO                     

P206                     

Final  analysis  of  the  steel: 
Sulphur 

Sulphur  in  coal  

There  appears  here  to  be  no  more  difference  than  would 
naturally  occur  daily  from  variations  of  charge  and  fuel. 

In  the  experience  of  the  General  Electric  Company,  at 
Schenectady,  N.  Y.,  with  a  wide  range  of  metallurgical  opera- 


16  POWDERED  COAL  AS  A  FUEL 

tions,  slag  and  clinker  gave  no  especial  difficulty.  In  steam 
generation,  they  became  serious  factors  only  under  heavy 
boiler  loads,  say  40  per  cent  above  normal,  and  indicated  the 
necessity  of  care  in  designing  and  operating  boiler  furnaces. 
"  With  powdered  coal,  furnace  temperatures  are  high; 
2700°  F.  or  more  is  not  uncommon  and  most  of  the  ash 
will  slag  when  hot.  It  was  aimed  at  Schenectady  to  slag 
as  much  as  possible,  drawing  off  the  fused  product  at  inter- 
vals. Fine  ash  passes  on  among  the  tubes.  The  slag  weighs 
5.72  per  cent  and  the  soot  3.41  per  cent  of  the  coal  that  made 
it.  This  coal  gives  11.26  per  cent  of  ash  in  the  laboratory, 
so  that  2  per  cent  must  have  gone  up  the  stack.  This  2 
per  cent  is  a  very  fine  white  powder,  scarcely  visible  at  the 
chimney  top.  The  slag,  which  weighs  114  Ib.  per  ton  of 
coal  fired,  contains  no  carbon  whatever.  At  moderate  loads, 
say  up  to  180  per  cent  of  normal,  it  is  drawn  out  once  during 
the  day  to  a  concrete  pit  containing  water.  The  pit  is 
cleaned  out  with  pick  and  shovel  the  next  morning.  This 
is  not  the  easiest  way  to  handle  slag.  If  there  were  a  cellar 
beneath  the  boiler  room  there  would  be  less  labor,  but  even 
as  it  is  the  work  is  not  difficult.  Water  hi  the  pit  is  essen- 
tial however. 

"  With  heavy  loads,  some  particles  of  slag  travel  with  the 
gas  current  and  cling  to  the  first  cold  surface  they  meet; 
that  is,  to  the  bottom  row  of  tubes.  If  this  slag  is  allowed 
to  accumulate  for  ten  hours,  it  will  choke  off  enough  of  the 
gas  passage  to  make  reduction  of  load  necessary.  This  was 
a  great  difficulty  at  first,  but  it  has  been  overcome.  The 
accumulation  can  be  blown  off  with  a  steam  jet  once  during 
the  forenoon  and  again  hi  the  afternoon.  This  does  not 
call  for  much  time  and  is  not  laborious.  Further  im- 
provement has  been  made  by  admitting  a  little  steam  at  the 
inlet  end  of  the  gas  passages.  This  steam  travels  with  the 
hot  air,  mingling  with  it  and  altering  the  character  of  the 
fire;  it  makes  slag  run  more  freely,  softening  and  decreasing 
the  quantity  that  clings  to  the  tubes.  It  pays  to  blow 
tubes  once  a  day.  Most  of  the  soot  goes  over  through  the 


COALS  SUITABLE  FOR  POWDERING  17 

second  pass  of  the  boiler  and  drops  in  the  back  chamber. 
The  bottom  of  that  chamber  has  been  paved,  giving  it  a 
pitch,  with  a  drain  pipe  leading  to  a  pit,  and  all  this  material 
is  washed  out  every  second  day  by  merely  opening  a  valve. 
The  soot,  however,  is  a  loss;  for  60  per  cent  of  it  is  carbon; 
that  is,  60  per  cent  of  3.41  per  cent  or  2  per  cent  of  the 
coal  is  unburned.  The  soot  is  light  and  fluffy,  weighing  18 
Ib.  per  cubic  foot.  No  good  use  for  it  has  been  found 
thus  far." 

Trouble  from  ash  in  metallurgical  operations  may  arise 
hi  the  combustion  chamber,  on  the  hearth,  or  in  the  flues. 
In  the  combustion  chamber,  slag  can  be  provided  for  by  the 
use  of  a  bed  of  cinders,  which  will  remain  loose  and  can  be 
pried  out.  On  the  hearth  of  a  reverberatory  furnace  the 
ash  forms  a  slag  which  can  be  drawn  off  with  other  im- 
purities. In  the  gas  flues,  control  of  the  heat  should  be 
such  as  to  keep  the  temperature  too  low  to  permit  the 
formation  of  slag.  In  any  case,  frequent  and  easy  access 
should  be  given  for  cleaning.  Checker  work  is,  according 
to  one  authority,  entirely  unsuitable  for  the  use  of  powdered 
coal.  It  will  slag  up  and  become  inoperative. 

In  locomotive  applications,  the  liquid  ash  runs  down  the 
under  side  of  the  main  arch  and  the  front  and  sides  of  the 
forward  combustion  zone  of  the  furnace  and  is  precipitated 
into  the  self-cleaning  slag-pan.  Here  it  accumulates  and 
is  air-cooled  and  solidified  into  a  button  of  slag  which  can 
be  dumped  by  opening  the  drop  bottom  doors. 

SUMMARY 

Ash  disposal  presents  problems  different  from  those  en- 
countered with  ordinary  coal.  They  are  to  be  handled  by 
proper  selection  of  fuel  (giving  attention  to  the  composition 
of  the  ash),  by  control  of  combustion,  by  running  off  liquid 
slag  and  by  the  mechanical  or  manual  cleaning  of  surfaces 
where  powder  or  clinker  may  accumulate. 


CHAPTER  III 
PREPARATION  OF  POWDERED  COAL 

HAVING  selected  a  proper  grade  of  coal,  usually  one  con- 
taining in  the  neighborhood  of  30  per  cent  of  volatile  matter, 
the  first  operation  is  generally  a  crushing  to  about  1-in. 
size. 

Fig.  1  shows  the  Jeffrey  single  roll  crusher.  It  is  so  con- 
structed as  to  withstand  the  severe  usage  to  which  it  is 


FIG.  1. — Jeffrey  Single-roll  Crusher. 

likely  to  be  subjected,  being  built  for  strength  and  endurance 
rather  than  with  any  over-refinement  of  parts. 

The  machine  consists  of  a  heavy  cast-iron  frame,  in  which 
are  mounted  a  crushing  roll  and  a  breaker  plate.  The 
breaker  plate  is  hinged  at  its  upper  end  and  is  held  in 
position  by  a  pair  of  adjusting  rods  at  the  lower  edge.  By 

18 


PREPARATION  OF  POWDERED  COAL  19 

this  means  the  clear  opening  between  the  breaker  plate 
shoe  and  the  surface  of  the  roll  can  be  varied  to  give  any 
size  of  product  required. 

A  clamping  effect  is  produced  by  proper  adjustment  of 
the  cross-rod  bolts  between  the  side  frames,  whereby  suf- 
ficient friction  may  be  brought  upon  the  hinged  breaker 
plate  to  eliminate  chattering  and  to  assist  the  safety  device. 

The  concave  breaker  plate  acting  in  conjunction  with  the 
roll  makes  a  form  of  maw,  with  a  very  small  angle  of  repose; 
hence  the  machine  will  readily  grip  a  large  lump  and  reduce 
it  to  such  size  as  will  pass  through  the  opening  between  the 
roll  and  plates.  A  countershaft,  mounted  directly  on  the 
machine,  drives  the  roll  through  a  pair  of  gears.  These 
are  made  so  heavy  that  sufficient  torque  is  obtained  to  start 
the  roll  under  all  conditions  of  load.  The  machine  cannot 
become  overloaded  or  clogged  up  under  any  volume  of  coal. 
It  makes  the  entire  reduction  in  a  single  operation. 

The  driving  pulley  is  not  keyed  to  the  shaft,  but  is 
mounted  on  a  separate  hub  which  it  drives  through  a  set  of 
wood  pins  inserted  in  holes  in  the  arms  of  the  pulley.  When 
any  undue  strain  comes  on  the  machine  from  any  cause, 
these  wood  pins  shear  off,  and  the  roll  stops  while  the  pulley 
keeps  on  revolving.  There  is  thus  formed  an  efficient  safety 
device  preventing  accidents  to  workmen.  After  the  cause 
of  the  trouble  has  been  removed,  new  wood  pins  put  the 
machine  again  in  operative  condition. 

A  pair  of  heavy  springs  is  placed  on  the  tension  rods. 
These  springs  do  not  move  under  ordinary  working  condi- 
tions; but  when  an  undue  pressure  comes  on  the  breaker 
plate,  they  act  as  a  cushion,  yielding  slightly,  taking  up  the 
inertia  of  the  parts  and  allowing  time  for  the  pins  to  shear 
without  breaking  more  important  elements  of  the  machine. 

Fig.  2  shows  the  "  S-A  "  improved  coal  crusher,  fitted 
with  the  patented  toggle  spring  release,  which  gives  maxi- 
mum pressure  between  the  rolls  when  they  are  in  normal 
operating  position.  On  the  ordinary  spring  type  of  crusher 
the  pressure  is  weakest  when  the  rolls  are  hi  normal  operating 


20 


POWDERED  COAL  AS  A  FUEL 


position.  The  two  types  of  crusher  operate  in  exactly  oppo- 
site ways.  Since  the  pressure  between  the  rolls  decreases 
as  the  rolls  are  separated,  pieces  of  iron  or  other  hard 
material  will  not  injure  the  rolls  of  the  "  improved  "  type 
of  crusher  as  they  do  the  rolls  of  the  ordinary  machine. 
The  pressure  between  the  rolls  is  regulated  by  nuts  that  are 
easily  accessible. 

Following  the  crushing,  the  coal  may  be  carried  (often 
by  belt  conveyor  and  elevator)  to  a  magnetic  separator 


FIG.  2.— S-A  Improved  Coal  Crusher. 

like  the  Ding  "  magnetic  pulley,"  which  removes  any  iron 
or  steel  scrap,  nuts,  pick  points,  pieces  of  iron,  bolts,  etc., 
that  would  interfere  with  pulverization. 

The  coal,  before  pulverizing,  should  be  well  dried,  down 
to  1  per  cent  or  less  of  moisture.  This  makes  it  pulverize 
better  and  burn  more  freely.  Coal  does  not  grind  well  if 
moisture  in  excess  of  this  is  present.  Nothing  is  lost  by 
drying  it  separately.  In  burning  coal,  the  moisture,  free 
or  combined,  must  be  disposed  of  either  in  the  process  of 
preparation  or  at  the  moment  of  combustion.  In  the  latter 


PREPARATION  OF  POWDERED  COAL  21 

case,  not  only  is  the  efficiency  of  the  furnace  lowered  by  the 
calorific  investment  in  the  superheated  steam  passing  out 
as  a  product,  but  the  temperature  of  the  furnace  is  lowered 
materially.  Drying  wet  coal  in  the  furnace  itself  is  doing 
this  necessary  part  of  the  work  in  the  most  expensive  place 
and  at  the  sacrifice  of  temperatures  which  may  be  essential 
to  the  industrial  process. 

In  the  practice  of  the  American  Iron  and  Steel  Co. 
(see  Chapter  VII),  attention  has  been  given  the  possibility 
of  using  undried  coal.  In  all  cases,  it  was  finally  deemed 
best  to  provide  for  drying.  The  drying  equipment  may  be 
arranged  for  intermittent  use,  if  apparatus  of  standard  size 
is  too  large  for  the  required  quantity  and  moisture  condition 
of  the  coal  available. 

First  cost  so  often  enters  into  the  selection  of  apparatus 
that  a  number  of  plants  without  dryers  have  been  intro- 
duced with  fairly  good  results,  maintained  even  when  the 
coal  contained  as  much  as  15  to  20  per  cent  of  water. 

Mr.  Lord  of  the  American  Iron  and  Steel  Co.  described 
a  visit  to  an  installation  in  Iowa  at  a  tune  when  there  was 
deep  snow  on  the  ground.  Into  this  snow  the  coal  was 
shoveled  after  dynamiting  it  out  of  the  car.  It  was  then 
elevated,  snow  and  all,  to  the  coal  hoppers  over  the  pulver- 
izing machines.  There  was  never  any  difficulty  in  the  opera- 
tion nor  any  trouble  in  maintaining  the  flame,  but  the 
procedure  was  certainly  not  favorable  to  good  economic 
results.  It  was  estimated  that  about  20  per  cent  more  coal 
was  used  in  the  furnaces  than  would  have  been  consumed 
with  adequate  drying  facilities :  and  the  power  consumption 
for  pulverizing  was  considered  to  be  about  50  per  cent  in 
excess  of  normal. 

The  only  reason  for  using  wet  coal  is  the  desire  to  keep 
down  the  initial  investment;  and  even  at  that,  says  Mr. 
Lord,  there  must  exist  the  assurance  of  commercially  dry 
coal  for  the  greater  part  of  the  time,  i.e.,  coal  carrying 
moisture  under  5  per  cent.  Provision  should  be  made  for 
protection  from  the  weather  as  much  as  possible  both  at  the 


22  POWDERED  COAL  AS  A  FUEL 

plant  and  in  transit.  One  concern  ships  its  coal  in  box 
cars.  Storage  will  drain  off  some  moisture,  but  slack  coal 
will  retain  15  per  cent  of  moisture  indefinitely,  unless  stirred 
up  and  brought  in  contact  with  air. 

Where  wet  coal  is  used,  and  in  all  low-temperature  appli- 
cations, an  igniting  flame  must  be  provided.  In  the  instal- 
lation just  referred  to  this  is  accomplished  by  a  grate  fire 
in  a  steel  box  18  in.  square  and  5  ft.  long,  and  12  in.  square 
inside  the  brick  lining.  The  powdered  coal  blowing  through 
this  small  box  comes  in  contact  with  the  grate  fire  flame 
and  hot  brick  walls  and  ignites  readily.  The  coal  on  this 
grate  is  replenished  by  particles  dropping  from  the  powdered 
coal  as  it  blows  through.  The  powder  which  falls  on  the 
grate  forms  coke  and  burns  freely.  Attention  is  required 
only  once  in  twenty-four  hours  for  cleaning  and  raking  out. 

The  possible  elimination  of  the  dryer  is  further  limited 
to  those  cases  where  a  type  of  grinding  machine  is  used  that 
will  handle  moist  coal.  Pulverizers  using  screens  for  the 
separation  of  the  coarse  and  fine  material  clog  up  imme- 
diately when  fed  with  moist  coal. 

THEORY   OF   DRYING 

To  dry  a  stated  weight  of  any  material  a  definite  number 
of  heat  units  must  be  used;  first,  to  raise  the  temperature 
of  the  material  to  212°;  second,  to  raise  the  temperature 
of  the  total  amount  of  water  contained  in  the  material 
to  212°;  and  third,  to  evaporate  such  part  of  the  water 
as  may  be  desired.  The  total  number  of  heat  units 
may  be  calculated  from  the  specific  heat  of  the  mate- 
rial, the  initial  and  final  percentages  of  moisture  and  the 
initial  temperature. 

If  then  the  heating  value  of  the  fuel  used  for  drying  and 
the  thermal  efficiency  of  the  apparatus  are  known,  the 
quantity  of  fuel  required  for  any  capacity  may  be  determined. 

When  the  composition  of  fuel  is  known,  we  may  then 
compute  how  much  air  is  theoretically  needed  to  burn  it. 
The  resulting  temperature  of  combustion,  however,  would  be 


PREPARATION  OF  POWDERED  COAL 


23 


much  too  high  for  dryer  operation.  A  large  excess  of  air 
must  be  introduced,  to  bring  the  temperature  of  gases  down 
to  about  1400°  F.,  at  which  temperature  they  enter  the  gas 
passage  of  the  dryer.  This  comparatively  high  temperature 
is  quickly  reduced  by  the  transfer  of  heat  through  the  steel 
shell  to  the  drying  coal.  When  these  gases  have  reached  the 
delivery  end  they  may  be  at  a  temperature  of  about  250°  F. 
If  (as  in  some  forms  of  machine)  they  then  pass  back  through 
the  cascading  coal,  they  are  still  further  reduced  in  tempera- 
ture, and  may  finally  leave  the  fan  at  about  100°  F.  In 
cooling,  the  gases  are  greatly  reduced  in  volume;  so  that  the 
velocity  through  the  shell  is  decreased  to  such  a  point  that 
comparatively  little  dust  is  carried  off. 

Indirect-fired  Rotary  Coal  Dryer.  The  Fuller-Lehigh 
indirect-fired  coal  dryer  (Fig.  3)  consists  of  an  axially 
inclined  cylindrical  shell  fitted  with  rollers  and  gearing 


FIG.  3.— Fuller-Lehigh  Indirect-fired  Dryer. 

which  rotate  the  shell  on  its  longitudinal  axis.  The  higher 
end  of  the  dryer  shell  terminates  in  a  brick  housing  which 
serves  to  support  the  stack  required  to  discharge  the  waste 
products  of  combustion  of  the  dryer  furnace,  including  the 


24  POWDERED  COAL  AS  A  FUEL 

water  vapor  given  off  by  the  moist  coal.  The  furnace  for 
heating  the  dryer  is  placed  between  the  stack  chamber  and 
the  hood.  The  furnace  may  be  provided  with  a  large  com- 
bustion chamber  through  which  the  dryer  shell  passes. 
The  entire  furnace  is  built  of  brick  and  the  walls  are  securely 
bound  together  by  means  of  buckstays  and  tie  rods. 

The  moist  coal  is  fed  into  the  dryer  shell  through  a  feed 
spout  located  in  the  stack  chamber.  This  spout  enters  the 
dryer  shell  and  delivers  the  coal  close  to  the  bottom.  A 
series  of  longitudinal  shelves  fastened  to  the  inside  of  the 
dryer  shell  lifts  the  coal  and  drops  it  through  the  current 
of  heated  air  passing  through  the  inside  of  fhe  dryer  shell. 
Since  the  revolving  shell  of  the  dryer  is  slightly  inclined 
downward  toward  the  discharge  end,  the  coal  travels  the 
entire  length  of  the  shell  and  is  finally  discharged  from  the 
lower  end. 

The  hot  gases  from  the  furnace  circulate  around  the  out- 
side of  the  dryer  shell,  passing  through  the  combustion 
chamber  of  the  furnace.  They  then  leave  the  combustion 
chamber  through  the  horizontal  breeching  and  enter  the  top 
of  the  hood  at  the  lower  end  of  the  dryer.  From  this  hood 
the  hot  gases  flow  to  the  interior  and  come  in  direct  contact 
with  the  coal  hi  the  dryer  shell.  After  they  pass  through 
the  interior,  the  hot  gases  enter  the  stack  chamber  at  the 
upper  end  of  the  dryer,  and  then  escape  to  the  atmosphere 
through  the  stack. 

No  flame  comes  in  direct  contact  with  the  coal  being 
dried,  and  there  is  absolutely  no  possibility  of  the  coal's  tak- 
ing fire  during  its  progress  through  the  dryer  shell.  No  fans 
are  used  in  connection  with  this  type  of  dryer,  as  the  stack 
draft  is  sufficient  to  move  the  gases  at  the  required  velocity. 

Ruggles-Coles  Dryer.  This  form  of  dryer,  illustrated  in 
Fig.  4,  consists  of  two  long  concentric  steel  plate  cylinders 
which  are  set  with  the  delivery  end  slightly  lower  than  the 
head  end.  Between  the  inner  cylinder,  which  acts  as  a  flue 
for  the  hot  furnace  gases,  and  the  outer  shell  is  the  space 
which  holds  the  material  to  be  dried.  The  two  cylinders 


PREPARATION  OF  POWDERED  COAL 


25 


are  rigidly  connected  midway  between  the  ends,  and  by 
placing  swinging  arms  between  this  center  and  each  end, 
allowance  is  made  for  the  unavoidable  expansion  and  con- 
traction due  to  differences 
in  temperature.     Such  con- 
struction entirely  prevents 
the  shearing   of    rivets    or 
loosening  of  joints. 

The  dryer  is  supported 
on  two  steel  tires  which  are 
rigidly  riveted  to  the  outer 
cylinder.  Each  tire  rests 
on  four  bearing  wheels 
made  of  chilled  iron.  These 
are  arranged  in  pairs  on 
rocker  arms,  which  are  sup- 
ported on  heavy  cast-iron 
bases.  Two  large  thrust 
wheels  are  provided  on  one 
of  the  bases  to  hold  the 
cylinder  tires  against  the 
wheels.  Set  screws  allow 
the  bearing  wheels  to  be 
adjusted  while  the  machine 
is  in  operation,  so  that  tires 
can  ride  centrally  on  them 
without  exerting  pressure 
on  the  thrust  wheels. 

Distribution  of  the 
weight  of  the  dryer  on 
eight  bearing  wheels,  each 
of  which  has  two  bearings, 

prevents  excessive  wear  or  overheating.  Riveted  to  and 
around  the  outer  cylinder  is  a  heavy  gear  which  engages 
with  a  pinion  keyed  to  the  driving  shaft.  This  shaft  may 
be  located  on  either  side  or  at  the  end  of  the  dryer,  as  may 
best  suit  local  conditions. 


26  POWDERED  COAL  AS  A  FUEL 

Lifting  plates  are  fastened  to  the  inside  of  the  outer 
shell,  running  parallel  with  the  axis  of  the  dryer  for  its  entire 
length.  The  revolving  of  the  dryer  causes  these  plates  to 
lift  the  coal  and  drop  it  on  the  hot  inner  shell.  By  the 
inclination  of  the  dryer  the  coal  is  carried  from  the  feed 
end  to  the  delivery  end.  On  the  inside  of  the  discharge 
head  at  the  delivery  end  there  are  riveted  buckets  which 
discharge  the  dried  coal  through  a  central  delivery  casting. 
At  the  feed  end  the  inner  cylinder  extends  beyond  and 
through  the  stationary  head  and  connects  directly  with  the 
flue  from  the  furnace.  This  inner  cylinder  forms  an  ex- 
tended combustion  chamber  for  the  unconsumed  gases  leav- 
ing the  furnace.  Doors  are  provided  at  both  ends  of  the 
dryer  for  inspection  purposes. 

Folio  wing  the  drying,  the  coal  is  pulverized  to  its  final 
degree  of  fineness.  With  the  best  type  of  machines  obtain- 
able for  this  purpose,  the  coal  and  its  contained  impurities 
may  readily  be  powdered  to  such  a  degree  that  under 
screening  tests  85  to  90  per  cent  will  pass  through  an 
aperture  Tw-in.  square,  while  the  total  residuum  left  upon 
a  screen  whose  apertures  are  TO-in.  square  will  be  only 
from  2|  to  5  per  cent;  and  even  this  residuum  would  pass 
through  screens  rw-m.  square.  It  must  be  borne  in  mind 
that  of  the  quantity  passing  the  apertures  ^b-in.  square 
there  is  a  high  percentage  of  absolute  dust  or  impalpable 
powder  not  commercially  measurable.  This  is  proven  by 
the  fact  that  in  tests  made  upon  calibrated  screens  of  ^r 
in.  square  aperture,  over  70  per  cent  still  passed  through. 
It  is  certainly  safe  to  assume,  therefore,  that  the  average 
volume  of  particles  will  be  less  than  that  of  a  cube  measur- 
ing ^ir-in.  on  the  side.  No  determination  is  made,  usually, 
of  fineness  below  200-mesh. 

The  total  number  of  particles  resulting  fron  the  powder- 
ing of  1  cu.in.  of  coal  to  spheres  ^  in.  in  diameter  is  over 
15  million.  Simple  calculation  on  this  basis  shows  that  while 
a  cubic  inch  of  coal  exposes  6  square  inches  for  absorption  and 
liberation  of  heat,  the  surface  exposed  for  the  same  purpose 


PREPARATION   OF  POWDERED   COAL  27 

by  the  powdered  coal  is  over  8  square  feet.  Since  no  fuel 
burns  until  it  is  heated  to  the  temperature  at  which  it 
develops  more  heat  than  it  receives,  the  advantage  of  this 
enormous  absorbing  and  delivering  surface  is  apparent. 
The  result  of  this  is  shown  in  the  clearness  and  uniformity 
of  the  flame  produced.  Where  coarse  particles  are  permitted 
to  enter  the  furnace,  distinct  sparkles  are  apparent.  These 
larger  particles  are  carried  beyond  the  region  of  oxygen 
supply  and  are  for  this  reason  not  fully  burned. 

At  the  Anaconda  plant  (see  Chapter  VI)  the  grinding  is 
done  so  that  from  93  to  97  per  cent  will  pass  through  100- 
mesh  and  79  to  82  per  cent  through  200-mesh.  Coals 
of  high  specific  gravity  will  grind  finer  in  an  impact  pulver- 
izer. In  cement  work,  there  is  no  gain  by  grinding  finer 
than  95  per  cent  through  100-mesh.  This  gives  from  75 
to  85  per  cent  through  200-mesh,  the  percentage  depending 
upon  the  physical  character  of  the  coal.  Coal  thus  pul- 
verized will  contain  a  high  percentage  of  fine  dust  practi- 
cally unmeasurable.  As  there  is  no  difficulty  in  burning 
coal  thus  prepared,  there  seems  to  be  no  good  reason  for 
pushing  pulverization  beyond  this  point.  Coal  can  be 
brought  to  this  condition  quite  cheaply,  and  the  mills  able 
to  so  this  work  have  large  capacity.  Higher  percentages 
may  be  obtained  by  the  sacrifice  of  capacity,  and  conse- 
quently of  grinding  economy.  The  standard  of  approxi- 
mately 85  per  cent  through  200-mesh  and  95  per  cent 
through  100-mesh  is  a  practicable  commercial  standard  and 
should  be  maintained. 

Fuller-Lehigh  Pulverizer  Mill.  In  this  mill  (Fig.  5)  the 
coal  is  fed  from  an  overhead  bin  by  means  of  a  feeder 
mounted  on  top  of  the  mill.  This  feeder  is  driven  direct 
from  the  mill  shaft  by  means  of  a  belt  running  on  a  pair 
of  three  step  cones,  which  permit  operative  adjustment. 
In  addition,  the  hopper  of  the  feeder  is  provided  with  a  slide, 
which  permits  the  operator  to  increase  or  decrease  the 
amount  of  coal  entering  the  feeder  hopper. 

The  coal  leaving  the  feeder  enters  the  pulverizing  zone 


28 


POWDERED  COAI,  AS  A  FUEL 


of  the  mill.  The  pulverizing  element  consists  of  four 
unattached  steel  balls  which  roll  in  a  stationary,  hori- 
zontal, concave-shaped  grinding  ring  (Fig.  6).  The  balls 
are  propelled  around  the  grinding  ring  by  means  of  four 
pushers  attached  to  four  equidistant  horizontal  arms  form- 
ing a  portion  of  the  yoke,  which  last  is  keyed  direct  to  the 
mill  shaft.  The  material  discharged  by  the  feeder  falls 


FIG.  5. — Fuller-Lehigh  Pulverizing  Mill. 

between  the  balls  and  the  grinding  ring  in  a  uniform  and 
continuous  stream,  and  is  reduced  to  the  desired  fineness 
in  one  operation. 

Those  mills  which  operate  with  fan  discharges  are  fitted 
with  two  fans.  One  of  these  fans  is  connected  in  the  separat- 
ing chamber  immediately  above  the  pulverizing  zone,  and 
the  other  fan  operates  in  the  fan  housing  immediately 
below  the  pulverizing  zone.  The  upper  fan  lifts  the  fine 


PREPARATION  OF  POWDERED  COAL  29 

particles  of  coal  from  the  grinding  zone  onto  the  chamber 
above  the  grinding  zone,  where  these  fine  particles  are  held 
in  suspension.  The  lower  fan  acts  as  an  exhauster,  and 
draws  the  finely  divided  particles  through  the  finishing 
screen  which  completely  encircles  the  separating  chamber. 
The  coal  leaving  the  separating  chamber  is  drawn  into  the 
lower  fan  housing,  from  which  it  is  discharged  through  the 
discharge  spout  by  the  action  of  the  lower  fan.  All  of  the 
coal  discharged  from  the  mill  is  finished  product  and  re- 
quires no  subsequent  screening. 


FIG.  6. — Fuller-Lehigh  Grinding  Ring. 

The  current  of  air  induced  by  the  action  of  the  lower  or 
discharge  fan  passes  over  the  pulverizing  zone,  and  out 
through  the  screen  surrounding  the  separating  chamber, 
thus  insuring  cool  operation  and  maximum  screening  effi- 
ciency. This  current  of  air  keeps  the  screen  perfectly 
clean  and  enables  the  mill  to  handle  coal  containing  a  con- 
siderable amount  of  moisture. 

When  the  mill  is  in  operation,  it  is  handling  only  a  limited 
amount  of  coal  at  any  one  time.  As  soon  as  the  coal  is 
reduced  to  the  desired  fineness,  it  is  lifted  out  of  the  pul- 
verizing zone  and  discharged.  As  the  crushing  force 


30  POWDERED  COAL  AS  A  FUEL 

is  applied  to  only  a  limited  amount  of  coal,  the  power 
required  to  operate  the  machine  is  reduced  to  a  minimum. 
Furthermore,  this  power  is  applied  directly  to  the  coal 
being  pulverized. 

In  order  to  insure  steady  operation,  every  mill  should  be 
provided  with  a  storage  bin  of  capacity  not  less  than  four  to 
six  times  the  hourly  capacity  of  the  mill.  Each  bin  should 
have  a  chute  or  feed  pipe,  6  or  8  in.  in  diameter,  to  permit 
the  coal  to  flow  from  the  bin  to  the  hopper  of  the  mill  feeder. 
This  chute  should  be  provided  with  a  gate  or  cut-out  slide 
placed  close  to  the  bin  so  that  the  flow  of  coal  through  the 
chute  may  be  controlled. 

A  platform  should  be  provided  around  the  mill  so  that 
the  operator  may  have  easy  access  to  the  feeder.  The 
floor  of  this  platform  should  be  about  3  in.  below  the  top 
flange  of  the  intermediate  section.  A  small  volume  of  air 
is  discharged  from  the  mill  with  the  finely  pulverized  coal. 
An  air  chamber  should  therefore  be  provided  in  connection 
with  the  conveyor  taking  the  coal  away  from  the  mill, 
to  permit  the  free  escape  of  the  air.  The  size  of  the  air 
chamber  varies  with  the  size  and  number  of  the  mills  dis- 
charging into  the  conveyer.  The  air  chamber  should  be 
proportioned  so  that  an  area  of  cross-section  of  1  sq.ft. 
is  provided  for  a  33-in.  mill  and  of  1^  sq.ft.  for  a  42-in. 
mill.  A  vent  pipe  about  10  in.  in  diameter  should  be  placed 
on  top  of  the  ah-  chamber.  This  vent  pipe  may  be  connected 
with  a  suitable  collecting  chamber  to  prevent  loss  of  dust 
from  this  source. 

In  order  to  facilitate  the  erection  of  the  mills  and  the 
renewal  of  worn  parts,  it  is  advisable  that  some  form  of  hoist 
be  placed  above  the  mill.  These  hoists  should  have  a  capac- 
ity of  three  (3)  tons  for  the  33-in.  mill,  and  four  (4)  tons  for 
the  42-in.  mill.  These  mills  are  capable  of  grinding  coal  to 
a  fineness  such  that  at  least  95  per  cent  will  pass  through  a 
100-mesh  screen. 

Raymond  Bros.'  Impact  Pulverizer.  The  Raymond  roller 
mill  (Fig.  7)  crushes  and  grinds  coal  by  gravity  and  centrif- 


PREPARATION  OF  POWDERED  COAL 


31 


ugal  force.  At  the  top  of  the  main  shaft  is  a  rigidly  attached 
spider  which  rotates  with  the  shaft.  To  the  arms  of  this 
the  rollers  are  pivotally  suspended  by  trunnions  carried  in 


FIG.  7.— Raymond  Roller  Mill. 

bearings  in  the  roller  housing.  Both  upper  and  lower 
bearings  of  the  roller  journals  within  the  journal  housings 
are  provided  with  long  removable  phosphor-bronze  bush- 
ings. The  rollers  are  made  of  cast  iron  with  chilled  faces. 


32  POWDERED  COAL  AS  A  FUEL 

Centrifugal  force  throws  the  rollers  outward  against  the 
steel  ball  ring.  A  plow  is  located  ahead  of  each  roller. 
This  constantly  throws  a  stream  of  coal  between  the  face  of 
the  roller  and  the  grinding  ring. 

In  the  mills  with  air  separation,  air  enters  the  mill 
through  a  series  of  tangential  openings  around  the  pulveriz- 
ing chamber  directly  under  the  grinding  ring  and  rollers. 
That  portion  of  the  coal  which  is  reduced  to  the  required 
fineness  by  one  passage  of  the  roller  is  instantly  carried 
up  by  the  air  current  to  the  receiving  receptacle.  That 
which  is  not  ground  sufficiently  fine  by  the  first  roller  is 
carried  between  the  succeeding  roller  and  the  grinding  ring 
to  receive  a  second  treatment. 

If  the  mill  is  kept  properly  filled  with  coal,  each  of  the 
plows  will  throw  a  constant  stream  between  the  two  grind- 
ing faces,  preventing  direct  contact  of  the  roller  and  the 
grinding  ring. 

In  this  mill  the  casting  supporting  the  plows  is  attached 
to  and  rotates  with  the  slow-speed  upright  shaft,  and  little 
power  is  required  to  raise  the  coal  and  throw  it  between  the 
crushing  surfaces  of  the  roller  and  the  grinding  ring.  The 
plows  can  be  removed  without  taking  the  mill  apart,  by 
simply  opening  one  of  the  doors.  The  construction  is 
such  that  the  faces  of  the  rollers  always  remain  parallel  with 
the  face  of  the  grinding  ring. 

POINTS   ON   AIR   SEPARATION 

To  obtain  perfect  separation  and  secure  an  impalpable 
powder,  the  air  must  be  expanded  and  rarefied  so  that  coarse 
particles  will  drop  out  of  the  current. 

To  obtain  a  large  quantity  of  impalpable  powder  per 
hour  by  air  separation,  a  large  volume  of  air  must  be  used 
in  order  to  lift  the  material. 

To  use  a  large  volume  of  air  and  yet  obtain  a  current 
so  light  as  to  carry  off  only  the  impalpable  powder,  there  must 
be  ample  room  to  expand  and  rarefy  the  air. 

To  secure  perfect  separation,  the  mechanism  for  expand- 


PREPARATION  OF  POWDERED   COAL 


33 


VOLUMES  AND  WEIGHTS  OF  DRY  AIR  AT  ATMOSPHERIC  PRESSURE, 
14.6963  POUNDS  PER  SQUARE  INCH 


Weight  in  pounds 
per  cubic  foot 


.080728 


1 +. 0020358  (T- 32) 


Volume  in  cubic  =  1  +.0020358(7-32) 
feet  per  pound 


.080728 


Temp. 
Deg.  F. 

Volume  as 
Compared 
with  Vol- 
ume at  32°. 

Weight  of 
1  Cu.ft. 
of  Air  in 
Pounds. 

Volume  of 
1  Lb.  of 
Air  in 
Cubic  Feet. 

Temp. 
Deg.  F. 

Volume  as 
Compared 
with  Vol- 
ume at  32°. 

Weight  of 
1  Cu.ft. 
of  Air  in 
Pounds. 

Volume  of 
1  Lb.  of 
Air  in 
Cubic  Feet. 

0 
10 
20 
30 

.9349 
.9552 
.9756 
.9959 

.08635 
.08451 
.  08275 
.08106 

11.581 
11.833 
12.085 
12.337 

700 
725 
750 
775 

2.3599 
2.4108 
2.4617 
2.5126 

.03421 
.03348 
.03279 
.03213 

29.233 
29  .  863 
30.494 
31.124 

32 
40 
50 
60 

1  .  0000 
1.0163 
1.0366 
1  .  0570 

.08073 
.07943 
.07788 
.07638 

12.387 
12.589 
12.841 
13.093 

800 
825 
850 
875 

2.5635 
2.6144 
2.6653 
2.7162 

.03149 
.03088 
.  03029 
.02972 

31.755 
32.385 
33.016 
33.646 

70 
80 
90 
100 

1  .  0774 
1.0977 
1.1181 
1  .  1384 

.07494 
.07354 
.07220 
.07091 

13.346 
13.598 
13.850 
14.102 

900 
925 
950 
975 

2.7671 
2.8180 
2.8689 
2.9198 

.02917 
.02864 
.02814 
.02765 

34  .  277 
34.907 
35.538 
36.168 

110 
120 
130 
140 

1.1588 
1.1791 
1.1995 
1.2199 

.06967 
.06847 
.06730 
.06618 

14.354 
14.606 
14.858 
15.111 

1000 
1025 
1050 
1075 

2.9707 
3.0216 
.   2.0725 
3.1234 

.02718 
.02672 
.02628 
.  02585 

36.799 
37.429 
38.060 
38.690 

150 
160 
170 
180 

1  .  2402 
1  .  2606 
1.2809 
1.3013 

.06509 
.06404 
.06302 
.06204 

15.363 
15.615 
15.867 
16.119 

1100 
1125 
1150 
1175 

3.1743 
3.2252 
3.2761 
3.3270 

.02543 
.  02503 
.02463 
.02426 

39.321 
39.952 
40.582 
41.212 

190 

200 
210 
212 

1.3217 
1.3420 
1.3624 
1.3664 

.06108 
.06015 
.05924 
.05908 

16.372 
16.624 
16.876 
16.926 

1200 
1225 
1250 
1275 

3.3779 
3.4288 
3.4797 
3.5306 

.02390 
.02354 
.02320 
.02286 

41.843 
42.473 
43.104 
43.734 

220 
230 
240 
250 

1  .  3827 
1.4031 
1.4234 
1.4438 

.05838 
.05754 
.05671 
.05591 

17.128 
17.381 
17.633 
17.885 

1300 
1325 
1350 
1375 

3.5815 
3  .  6323 
3.6832 
3.7341 

.02254 
.02222 
.02192 
.02162 

44.365 
44.994 
45.625 
46.255 

260 
270 
280 
290 

1.4642 
1.4845 
1  .  5049 
1  .  5252 

.05513 
.05438 
.05364 
.  05293 

18.137 
18.389 
18.641 
18.893 

1400 
1425 
1450 
1475 

3  .  7850 
3.8359 
3  .  8868 
3.9377 

.02133 
.02104 
.  02077 
.02051 

46.886 
47.517 
48.147 
48.777 

300 
320 
340 
360 

1  .  5456 
1  .  5863 
1  .  6270 
1.6677 

.05223 
.05089 
.04962 
.04841 

19.145 
19  .  649 
20.154 
20.659 

1500 
1550 
1600 
1650 

3.9886 
4  .  0904 
4.1922 
4  .  2940 

.  02024 
.01974 
.01926 
.01880 

49.408 
50.669 
51.930 
53.191 

380 
400 
420 
440 

1  .  7085 
1  .  7492 
1  .  7899 
1.8306 

.04725 
.04615 
.04510 
.04410 

21.164 
21.668 
22.172 
22.676 

1700 
1750 
1800 
1850 

4  .  3958 
4.4976 
4.5993 
4.7011 

.01836 
.01795 
.01755 
.01717 

54.452 
55.713 
56.973 
58.234 

460 
480 
500 
520 

1.8713 
1.9120 
1.9528 
1.9935 

.04314 
.04222 
.04134 
.  04050 

23.180 
23.685 
24.189 
24.694 

1900 
2000 
2100 
2200 

4  .  8029 
5  .  0065 
5.2101 
5.4137 

.01681 
.01612 
.01549 
.01491 

59  .  495 
62.017 
64.539 
67.061 

540 

560 
580 
600 

2.0342 
2  .  0749 
2.1156 
2.1563 

.  03969 
.03891 
.03816 
.03744 

25.198 
25  .  702 
26.207 
26.711 

2300 
2400 
2500 
2600 

5.6173 
5.8208 
6.0244 
6  .  2280 

.01437 
.01387 
.01340 
.01296 

69.583 
72.104 
74.626 
77.148 

620 

640 
660 
680 

2.1971 
2.2378 
2.2785 
2.3192 

.03674 
.03607 
.03543 
.03481 

27.216 
27.720 
28  .  224 
28.729 

2700 
2800 
2900 
3000 

6.4316 
6.6352 
6  .  8388 
7  .  0424 

.01255 
.01217 
.01180 
.01146 

79.670 
82.192 
84.714 
87.236 

34 


POWDERED   COAL  AS  A  FUEL 


ing  and  rarefying  the  air  must  be  such  that  the  coarse  par- 
ticles will  drop  out  of  the  current  and  not  carry  the  fine 
powder  with  them. 

The  apparatus  must  be  so  constructed  that  the  coarse 
particles  or  tailings  will  drop  by  gravity  into  the  contracted 
portion  of  the  separator,  where  the  blast  is  stronger,  in  order 
that  they  may  pass  out  through  the  tailing  spout  or  back  into 
the  pulverizer  without  carrying  the  fine  material  with  them. 

The  nearer  the  condition  within  the  air  space  of  the 
apparatus  can  be  made  to  approach  a  vacuum,  the  finer 
will  be  the  separation. 

COST  OF  LABOR  AND  MAINTENANCE  FOR   POWDERED  COAL 
WITH  RAYMOND  PULVERIZERS 


Total 
Cost 
per  Ton, 

Cents. 

Capacity 
in  Tons 

Hour. 

Per  Cent 
100- 
mesh. 

Per  Cent 
200- 
mesh. 

Total 
Horse- 
power. 

Horse- 
power 
per  Ton. 

LABOR 

Main- 
tenance 
Cost,  per 
Ton, 
Cents. 

Men  at 
$2  per 
Day. 

Cost  per 
Ton, 
Cents. 

11.0 

11.8 
7.6 
8.4 
6.0 
6.8 
5.0 
5.8 
4.3 
5.1 
3.0 
5.8 
2.6 
4.2 

2 
2 
3 
3 
4 
4 
5 
5 
6 
6 
10 
10 
25 
25 

95 

82 

95 
82 
95 
82 
95 
82 
95 
82 
95 
82 
95 
82 
95 

45 
60 
60 
85 
75 
120 
85 
145 
120 
170 
170 
255 
425 
680 

22.5 
30.0 
20.0 
28.3 
18.8 
30.0 
17.0 
29.0 
20.0 
28.2 
17.0 
25.5 
17.0 
27.2 

1 
1 
1 
1 

1 

2 
2 
3 

10.0 
10.0 
6.6 
6.6 
5.0 
5.0 
4.0 
4.0 
3.3 
3.3 
2.0 
4.0 
1.6 
2.4 

1.0 
1.8 
1.0 
1.8 
1.0 
1.8 
1.0 
1.8 
1.0 
1.8 
1.0 
1.8 
1.0 
1.8 

95 

95 

95 

95 

95 

95 

The  cost  in  the  above  table  does  not  include  that  of  power, 
as  this  is  variable  with  local  conditions.  The  cost  of  main- 
tenance when  grinding  95  per  cent  100-mesh  is  much  less 
than  when  grinding  95  per  cent  200-mesh.  As  a  general 
rule,  doubling  the  fineness  of  the  mesh  doubles  the  main- 
tenance cost. 


PREPARATION  OF  POWDERED  COAL 


35 


The  Jeffrey  Swing  Hammer  Pulverizer.  In  the  past  few 
years,  the  swing  hammer  pulverizer  has  proved  itself 
to  be  an  efficient  machine  for  the  pulverizing  of  coal  and 
other  materials. 

The  machine  shown  in  Fig.  8  pulverizes  coal  by  strik- 
ing it  while  in  suspension,  as  opposed  to  the  rubbing  and 
abrasion  mills  which  roll  and  mash  the  coal  between  hard 
surfaces.  The  material  to  be  reduced  is  fed  in  near  the 
top  of  the  machine,  and  in  falling  comes  in  contact  with 


FIG.  8. — Jeffrey  Swing-hammer  Pulverizer. 

rapidly  revolving  hammers,  which  drive  the  coal  against  the 
breaker  plates,  from  which  it  rebounds  again  into  the  paths 
of  the  hammers. 

Fineness  is  to  a  large  extent  determined  by  the  inten- 
sity of  the  blow,  and  hence  different  degrees  of  reduction 
may  be  had  by  simply  varying  the  speed  of  the  machine. 
Different  materials  and  different  conditions  of  the  same 
material  as  to  temperature,  moisture,  etc.,  will  result  in 
corresponding  differences  in  the  degree  of  reduction,  so  that 
it  is  impossible  to  predict  beforehand  the  results  to  be  ex- 
pected from  any  particular  material  until  it  is  tried  out. 

The  supply  of  coal  may  be  fed  by  hand  or  discharged 
directly  from  a  large  bin,  some  sort  of  automatic  feeding 


36 


POWDERED  COAL  AS  A  FUEL 


device  being  desirable.  The  coal  falls  down  on  a  sloping 
breaker  plate  where  it  is  engaged  by  the  rapidly  moving 
hammers.  The  partially  reduced  material  immediately 
passes  over  the  cage  of  screen  bars.  Here  all  that  is  suf- 
ficiently fine  will  pass  through,  while  the  residue  is  car- 
ried around  the  machine  for  a  second  operation.  The  top 
breaker  plate  materially  assists  in  reducing  oversize  coal. 

The  Aero  Pulverizer.  The  Aero  pulverizer,  Fig.  9, 
consists  of  three  interiorly  communicating  chambers  (type 
"  E  "  has  four)  of  successively  increasing  diameters,  in  which 
revolve  paddles  on  arms  of  correspondingly  increasing 


FIG.  9. — Aero  Pulverizer. 

lengths.  The  separate  chambers  are  in  fact  separate  pul- 
verizers on  a  single  shaft,  each  succeeding  pulverizer  having 
greater  speed  at  its  periphery  and  therefore  greater  power  for 
fine  grinding.  An  additional  chamber  contains  a  fan,  the 
function  of  which  is  to  draw  the  more  finely  pulverized  coal 
successively  from  one  chamber  to  the  next,  and  to  deliver 
it  through  a  pipe  connection  to  the  furnace  under  the  impetus 
of  a  forced  draft.  The  separate  pulverizers  and  fan  are 
enclosed  in  one  steel  cylinder.  An  adjustable  feed  mechan- 
ism controls  and  varies  the  quantity  of  coal  admitted  and 
delivered  by  the  machine. 

The  feed  mechanism  is  exact  and  uniform  in  its  opera- 
tion and  is  easily  adjusted  to  meet  even  minute  variations  in 


PREPARATION  OF  POWDERED  COAL 


37 


the  fuel  requirement.  Two  adjustable  inlets  in  the  feed 
mechanism  admit  the  air  required  for  fine  grinding.  An 
auxiliary  inlet  between  the  last  grinding  chamber  and  the 
fan,  controlled  by  a  damper,  admits  such  additional  air 
as  is  required  for  combustion.  The  air  dampers,  with  the 
feed  control,  give  regulation  of  the  flame  within  a  wide 
range. 

The  discharge  may  be  either  right  orl  eft-hand  as  desired. 
The  pulverizer  is  dust-proof,  and  is  arranged  for  easy 
repair  to  the  parts  susceptible  to  water.  The  cost  of  such 
repair  is  small.  The  pulverizer  may  be  located  either  in 
front  of  the  furnace  or  at  either  side,  or  above,  or  below. 

The  connection  between  the  pulverizer  and  the  furnace 
is  usually  a  galvanized  iron  pipe.  No  additional  feeding  or 
mixing  apparatus  is  necessary,  as  the  powdered  coal  and  air 
are  intimately  mixed  in  the  pulverizer.  The  furnace  end 
of  the  discharge  pipe  is  made  of  such  size  and  shape  as  the 
furnace  construction  may  require. 

STANDARD  SIZES  OF  AERO  PULVERIZERS 


Normal 

Horse- 

Size. 

Weight, 
Pounds. 

Height, 
Inches. 

Floor  Space, 
Inches. 

Output  Soft 
Coal,  Pounds 
per  Hour. 

R.p.m. 

Horse- 
power 
Consump- 
tion. 

power  of 
Motor 
Recom- 
mended. 

A 

2250 

28f 

61f  X27f 

600 

2050 

10 

15 

B 

4000 

45 

77|  X  29 

1000 

1750 

14 

25 

C 

4500 

.46f 

78fx29 

1800 

1550 

25 

35 

D 

5900 

50 

89   X33 

3000 

1450 

40 

50 

Bonnot  Pulverizer.  The  Bonnot  pulverizer,  Fig.  10, 
consists  of  a  heavy  one-piece  main  frame,  which  contains 
the  grinding  parts,  consisting  of  grinding  rolls  and  roll 
head  or  driver.  The  main  frame  is  bored  and  lined  with  a 
removable  steel  bushing  forming  a  seat  for  the  grinding  ring. 

The  grinding  ring  stands  vertically  and  is  held  in  place 
by  two  large  clamp  bolts  extending  through  to  the  rear  of 
the  base.  The  rolls  revolve  around  the  inner  side  of  the 


38 


POWDERED  COAL  AS  A  FUEL 


ring  and  are  held  in  place  and  driven  by  the  head  or  driver. 
The  driver  is  recessed  to  receive  the  rolls  and  is  so  shaped 
as  to  converge  the  coal  on  the  track  in  front  of  the  rolls.  It 
is  a  high-carbon  steel  casting  with  hard-wearing  surfaces. 


PIG.  10. — Bonnot  Pulverizer. 

There  is  a  large  cover  plate  on  the  side  of  the  main  frame, 
through  which  the  driver,  rolls  and  grinding  ring  may  be 
removed  without  disturbing  other  parts. 

This  pulverizer  is  particularly  adapted  to  use  with  a 
separator,  owing  to  the  fact  that  the  grinding  parts  revolve 


PREPARATION  OF  POWDERED  COAL  39 

in  a  vertical  plane,  and  throw  a  constant  stream  of  ground 
coal  upward  against  the  separator. 

The  base  of  the  separator  is  attached  to  the  top  of  the 
grinding  chamber,  and  is  made  with  the  sides  flaring  or 
diverging  so  as  to  form  a  large  air  chamber  into  which  the 
coal  is  thrown  in  a  constant  stream  by  the  grinding  parts. 
The  air  current  entering  at  the  bottom  of  the  separator 
passes  upward  and  carries  away  the  fine  material.  Because 
of  the  increased  area  toward  the  top  of  the  separator,  the 
velocity  of  the  air  current  is  there  reduced.  This  allows  the 
coarser  material  to  fall  back  into  the  grinding  chamber, 
while  the  fine  material  is  carried  upward. 

A  feature  of  this  separator  is  an  interior  flue  on  each  side, 
by  means  of  which  a  considerable  range  of  fineness  may  be 
secured.  These  flues  are  hinged  at  the  bottom  and  adjusted 
by  a  lever  on  the  outside  of  the  separator.  To  obtain  a 
fine  product,  the  flues  are  inclined  outward  to  a  position 
parallel  with  the  walls  of  the  separator;  while  for  obtain- 
ing a  coarse  product,  they  are  set  in  a  vertical  position. 
It  is  possible,  without  changing  the  speed  of  the  fan,  to 
obtain  a  range  of  fineness,  from  98  per  cent  through  a  200- 
mesh  and  practically  all  through  100-mesh,  to  a  product 
of  which  50  per  cent  will  pass  100-mesh,  and  the  balance 
range  in  size  to  16-mesh  or  even  coarser.  The  velocity 
of  the  air  current  and  the  position  of  the  flues  will  determine 
the  degree  of  fineness. 

The  air  current  carrying  the  impalpable  material  passes 
from  the  separator  through  a  pipe  to  the  collector,  entering 
the  latter  on  the  side,  in  a  horizontal  direction. 

Since  the  collector  is  polygonal  in  shape,  the  various 
sides  or  faces  break  up  and  change  the  direction  of  the  air 
current,  meanwhile  reducing  the  velocity.  This  allows  the 
material  in  suspension  to  drop  to  the  discharge  pipe  at  the 
bottom  of  the  collector.  At  the  top  of  the  collector,  a  con- 
nection leads  to  a  small  auxiliary  collector  of  similar  shape, 
which  is  designed  to  remove  any  moderately  fine  material 
still  remaining  in  suspension. 


40  POWDERED  COAL  AS  A  FUEL 

The  Tube  Mill.  The  Bonnot  tube  mill  consists  of  a 
cylinder  of  steel  plate,  usually  made  from  4  to  5  ft.  ha 
diameter  and  hi  any  length  from  15  to  25  ft.  The  heads 
of  the  mill  are  lined  with  hard  iron  plates  and  the  cylinder 
with  either  silex  stone  or  hard  iron  as  may  be  desired.  The 
cylinder  is  supported  at  each  end  on  large  gudgeons,  which 
are  cast  solid  with  the  circular  steel  heads  forming  the  ends 
of  the  cylinder.  These  heads  are  bolted  to  heavy  cast 
rings  running  on  large  bearings.  The  mill  is  driven  by 
means  of  a  countershaft  having  a  pinion  engaging  with  a 
large  spur  gear  attached  to  the  cylinder. 


FIG.  11.— Bonnot  Tube  Mill. 

The  material  is  fed  into  the  cylinder  by  means  of  a  worm 
in  the  hollow  gudgeon  at  one  end  of  the  mill.  The  feeder 
is  an  automatic  regulating  device  and  can  be  adjusted  in- 
stantly to  give  any  desired  capacity  up  to  50  per  cent 
above  the  normal  capacity  of  the  mill.  It  is  supported  by  a 
heavy  bracket  bolted  to  the  main  bearing.  It  is  driven 
direct,  by  means  of  gearing  from  the  end  of  the  gudgeon. 

The  material  is  discharged  from  the  mill  either  through 
the  hollow  gudgeon  at  the  discharge  end,  or  through  the  end 
of  the  cylinder  by  means  of  slotted  holes  through  the  liners 
and  discharge  head.  When  the  latter  arrangement  is  used, 
a  close-fitting  cast-iron  dust  housing  is  provided,  which  is 


PREPARATION  OF  POWDERED  COAL  41 

supported  by  brackets  resting  on  the  main  bearing.  The 
fineness  of  the  product  obtained  is  regulated  by  the  amount  of 
material  fed  into  the  mill. 

This  tube  or  pebble  mill  is  economical  with  regard  to 
wear  owing  to  the  fact  that  it  is  a  slow-running  machine 
and  grinding  is  done  by  the  rolling  or  impact  of  flint  pebbles, 
with  which  the  cylinder  is  filled  about  one-half  full.  Such 
materials  as  cement  clinker  and  similarly  hard,  gritty  sub- 
stances are  handled  advantageously  by  the  tube  mill.  The 
efficiency  of  the  mill  is  not  reduced  by  wear  on  the  pebbles 
and  lining,  provided  the  normal  charge  of  pebbles  is  main- 
tained. Some  tube  mills  use  lengths  of  pipe  or  tubing, 
or  steel-plate  punchings,  instead  of  loose  pebbles.  All  grind 
very  fine;  so  fine,  in  fact,  as  to  be  frequently  expensive 
in  power. 

CAPACITIES  OF  TUBE   MILLS 

A  5  by  22  ft.  mill  with  Silex  lining,  containing  6  tons  of 
pebbles,  fed  with  coal  not  exceeding  J  in.  size,  ground  1J 
to  2  tons  per  hour,  94  per  cent  to  100-mesh. 

The  same  mill,  with  pebbles  and  4-ft.  tubes,  ground 
2 1  tons  per  hour,  95  per  cent  to  100-mesh. 

A  No.  18  Kominuter  mill  grinding  10  to  12  tons  per  hour 
sent  all  tailings  which  would  pass  over  a  £  by  A-in.  screen 
to  a  Bonnot  tube  mill  loaded  with  punchings.  Two  such 
mills,  5  by  9  ft.,  ground  4J  tons  of  the  tailings  per  hour, 
96  per  cent  to  100  mesh. 

A  5  by  22  ft.  Silex-lined  mill  loaded  with  11  tons  of  slugs 
ground  3|  to  4  tons  per  hour,  96  per  cent  to  100  mesh. 
A  precisely  similar  mill  on  a  succeeding  day  produced  this 
same  fineness  on  4|  to  5J  tons  per  hour. 


CHAPTER  IV 
FEEDING  AND  BURNING  POWDERED  COAL 

IN  a  paper  before  the  American  Institute  of  Mining 
Engineers,  1913,  Mr.  H.  R.  Barnhurst  lays  down  certain 
principles  of  which  the  following  is  an  abstract:  When 
coal  is  shoveled  or  fed  in  bulk,  a  certain  degree  of  com- 
minution or  pulverization  takes  place  in  the  fire  as  an  inci- 
dent of  combustion.  Coal  does  not  burn  in  lumps,  but  its 
ash  comes  away  pulverized.  This  gradual  pulverization 
occurs  in  the  fire  at  the  expense  of  some  of  the  heat  units 
in  the  fuel.  As  this  pulverization  is  accomplished  slowly, 
it  is  necessary  to  supply  a  large  grate  area  so  that  the  col- 
lective surface  exposed  for  disengagement  of  heat  shall  be 
sufficient  for  the  purpose  for  which  the  fire  is  used. 

To  be  classed  as  a  fuel  a  material  must  be  able  to  give 
out  more  heat  than  it  receives.  No  fuel  will  burn  until  its 
particles  are  brought  to  this  self-supporting  condition  by  the 
heat  absorbed  from  particles  previously  burned.  Not 
only  this,  but  the  oxygen  of  the  air  must  be  heated  likewise 
to  a  combining  temperature.  This  involves  heating  the 
accompanying  nitrogen.  This  heat  must  be  passed  from 
substance  to  substance  in  increments  small  in  themselves 
but  collectively  as  large  as  the  occasion  demands. 

In  the  use  of  powdered  coal  the  fuel  is  already  prepared 
for  the  absorption  and  evolution  of  heat.  In  addition,  it  is 
aimed  to  prepare  the  air,  by  a  practically  similar  subdi- 
vision, for  joining  in  the  process.  The  delivery  of  coal  and 
air  to  the  furnace  must  be  controlled  so  that  the  proper 
amount  of  each  will  be  secured. 

The  sequence  of  events  in  combustion  is  as  follows :  the 
volatile  elements  of  the  fuel  are  first  disengaged.  These 
highly  combustible  hydrocarbons  combine  with  the  oxygen 

42 


FEEDING  AND  BURNING  POWDERED  COAL          43 

of  the  air,  burning  to  C02  and  H2O,  and  disengaging  heat 
enough  to  bring  up  to  an  ignition  temperature  the  fixed 
carbon  components. 

It  is  evident  that  comparatively  large  masses  of  fuel 
supplied  with  large  volumes  of  air  will,  for  reasons  simply 
mechanical,  fail  in  efficiency.  This  is  more  particularly 
the  case  when  large  contents  of  volatile  matter  are  suddenly 
set  free  by  contact  with  another  mass  of  incandescent  fuel 
and  with  heated  surroundings.  Under  such  conditions 
it  is  impossible  to  get  the  best  results  from  any  fuel.  The 
sweeping-off  of  volumes  of  volatile  gases  by  large  volumes 
of  insufficiently  heated  air  produces  smoke.  This  smoke 
represents  but  a  small  weight  of  carbon  unburned,  but 
may  indicate  a  condition  under  which  a  large  quantity  of 
gases  passes  off  uncombined.  A  heavy  draft  pressure  accent- 
uates this  condition,  and  records  are  plentiful  of  the  passage 
through  fires  of  large  excesses  of  oxygen  which  has  failed  of 
its  duty  from  lack  of  heat  preparatory  to  combination. 

A  pulverized  fuel,  the  particles  of  which  are  each  sur- 
sounded  by  a  minute  envelope  of  air,  sufficient  thoroughly 
to  burn  them,  is  an  ideal  fuel  under  ideal  conditions.  In 
projecting  a  cloud  of  such  fuel  into  a  highly  heated  chamber, 
each  particle  because  of  its  opacity  becomes  an  absorbent 
of  heat,  radiating  not  only  from  the  chamber  walls,  but  from 
each  neighboring  particle  as  it  inflames.  This  inflammation 
progresses  with  rapidity  almost  inconceivable.  Pulverized 
fuel  injected  with  its  air  supply  at  a  speed  of  several  thou- 
sand feet  per  minute  inflames  right  up  against  the  delivery 
nozzle,  the  flame  playing  about  its  mouth.  This  is  best 
accomplished  by  avoiding  high  pressure  in  projecting  the 
fuel.  The  final  combination  of  air  and  fuel  occurs  at  the 
instant  of  projection  into  the  furnace.  The  air  carrying 
the  fuel  expands  as  soon  as  it  is  heated.  This  expansion 
is  of  course  due  to  the  increase  in  temperature,  and  explains 
the  large  volume  assumed  by  the  flame  on  leaving  the  point 
of  entrance. 

The  powdered  coal  problem  is  one  of  combustion  under 


44  POWDERED  COAL  AS  A  FUEL 

peculiar  conditions.  The  burning  of  powdered  coal  differs 
from  the  burning  of  solid  fuel  in  one  essential  particular. 
In  the  combustion  of  coal  in  commercial  sizes  lying  on  the 
grate,  the  air  for  combustion  passes  between  the  pieces  of 
coal  and  the  products  of  combustion  pass  off  in  the  flue. 
Powdered  coal  does  not  burn  under  such  conditions,  as  the 
particles  are  so  fine  that  sufficient  air  for  combustion  could 
not  reach  the  coal  through  crevices  between  the  particles 
lying  in  a  solid  bed.  To  burn  powdered  coal  successfully, 
it  must  be  burned  while  in  suspension  in  the  air.  In  such 
a  position  each  particle  is  surrounded  by  air  which  supports 
the  combustion.  The  form  of  furnace  used  in  making  Port- 
land cement  is  favorable  for  combustion  in  suspension, 
since  it  is  very  long  and  affords  plenty  of  room. 

Contact  of  the  particles  of  coal  dust  with  other  bodies 
results  in  the  lowering  of  temperature  to  such  an  extent  as  to 
make  combustion  impossible.  There  is  a  more  or  less  com- 
plete loss  of  any  fuel  which  falls  down  to  the  grate.  The 
time  for  combustion  is  evidently  increased  as  the  size  of  the 
dust  particle  is  increased;  from  which  it  follows  that  the  finer 
the  grinding,  other  things  being  equal,  the  quicker  and  more 
perfect  will  be  the  combustion. 

In  the  early  days  of  development  of  the  process  of  pow- 
dered coal  burning,  ignorance  of  the  necessity  of  fine  grind- 
ing was  the  cause  of  many  failures  in  burning  the  fuel.  In 
the  cement  industry,  special  devices  for  regulating  the  supply 
of  air  for  injecting  the  fuel  are  supplied,  but  no  special 
controlling  apparatus  is  supplied  for  the  air  which  enters 
the  kiln  through  the  various  openings  around  the  hood. 
It  would  be  difficult  to  control  the  admission  of  such  air: 
but  by  increasing  the  fuel  charge,  it  is  possible  to  bring  the 
air  supply  down  to  any  relative  proportion  desired. 

Patents  taken  out  many  years  ago  for  the  burning  of 
powdered  coal  under  boilers  and  in  various  arts  show  vari- 
ations in  the  kinds  of  pulverizers  and  feeding  devices,  and 
also  foreshadow  the  idea  of  delivering  the  powdered  coal  into 
the  furnace  by  a  jet  of  air  or  steam. 


FEEDING  AND  BURNING  POWDERED   COAL  45 

The  perfect  combustion  of  1  Ib.  of  carbon  demands  2f 
Ib.  of  oxygen.  This  is  contained  in  11.6  Ib.  of  air,  or  about 
154  cu.ft. ;  should  less  than  this  quantity  of  air  be  supplied, 
a  proportionate  amount  of  fuel  will  be  burned  to  CO,  with 
a  loss  of  two-thirds  of  its  potential  efficiency.  A  part  of 
this  loss  may  be  regained  by  contact  with  heated  oxygen; 
or  the  CO  may  pass  on  and  burn  in  the  chimney,  doing  no 
good.  Carbon  monoxide  is  necessarily  formed  in  an  atmos- 
phere of  gases  deficient  in  oxygen,  and  its  formation  renders 
still  more  difficult  the  further  establishment  of  active  com- 
bustion. 

The  temperatures  attainable  with  powdered  coal  are  very 
high,  so  high  that  excess  air  is  commonly  admitted  in  propor- 
tions ranging  between  50  and  100  per  cent.  This  excess  air 
dilutes  the  gases  resulting  from  combustion  and  lowers 
the  temperature. 

The  following  table  shows  the  temperatures  attained 
in  the  perfect  combustion  of  pure  carbon  with  varying 
amounts  of  air: 

Deg.  F. 

1  Ib.  carbon  with  11.6    Ib.  air  (normal) 3990 

1  Ib.  carbon  with  12.76  Ib.  air  (  10%  excess) 3747 

1  Ib.  carbon  with  13.92  Ib.  air  (  20%  excess) 3526 

1  Ib.  carbon  with  15.08  Ib.  air  (  30%  excess) 3333 

1  Ib.  carbon  with  16.24  Ib.  air  (  40%  excess) 3153 

1  Ib.  carbon  with  17.40  Ib.  air  (  50%  excess) 3002 

1  Ib.  carbon  with  18.56  Ib.  air  (  60%  excess) 2849 

1  Ib.  carbon  with  19.72  Ib.  air  (  70%  excess) 2725 

1  Ib.  carbon  with  20.88  Ib.  air  (  80%  excess) 2509 

1  Ib.  carbon  with  22.04  Ib.  air  (  90%  excess) 2847 

1  Ib.  carbon  with  23.20  Ib.  air  (100%  excess) 2345 

In  practice,  the  furnace  tender  soon  becomes  educated 
to  the  point  of  judging  whether  a  fire  is  hot  enough  by  its 
color  and  by  the  length  of  the  flame.  The  more  perfect 
the  conditions  the  shorter  and  whiter  the  flame. 

Some  fuels  can  be  burned  almost  without  care  on  the 
part  of  the  operator;  gas  is  one  and  oil  another.  There  is 
no  economy  in  such  ways  of  operating,  but  the  furnace  is 


46  POWDERED  COAL  AS  A  FUEL 

undeniably  hot.  Mr.  A.  S.  Mann,  of  the  General  Electric 
Company,  remarked:  "  I  recall  an  instance  where  an  oil 
man  wanted  a  really  good  fire  and  had  no  oil  to  waste.  He 
watched  the  fire  all  the  time  and  kept  it  right;  if  he  eased 
off  his  oil  a  trifle  he  cut  down  his  air  too  and  did  not  forget 
to  look  at  the  chimney,  top  and  bottom.  Such  work 
always  pays,  whatever  the  fuel  may  be. 

"  Powdered  coal  is  not  a  fuel  that  can  be  left  for  half 
a  day  to  itself  while  the  fireman  goes  to  grind  his  knife 
and  pare  an  apple. "  Fires  may  run  all  day  with  no  change 
in  adjustment  whatever,  but  somebody  should  always 
know  that  they  are  right;  and  the  fire  should  be  looked  after 
every  half  hour  or  so.  There  is  always  slag  and  some  fine 
ash  forming;  it  is  well  to  know  where  these  are  going.  On 
the  other  hand  a  wrong  adjustment  of  either  coal  or  air 
soon  makes  itself  apparent.  Powdered  coal  burns  best  with 
a  supply  of  200  cu.ft.  of  air  for  each  pound.  It  can  burn, 
and  burn  clearly,  with  160  ft.  and  even  less,  but  the  excess 
pays.  When  the  supply  exceeds  200  ft.  efficiency  begins 
to  fall.  There  is  a  noticeable  loss  even  at  208  ft.  The 
eye  cannot  discriminate  between  a  200-ft.  and  a  208-ft. 
fire,  but  it  can  recognize  a  250-ft.  or  even  a  220-ft.  blaze. 
There  is  a  marked  change  in  the  appearance;  and  unless  a 
"  cutting  "  fire  is  really  wanted,  there  is  no  excuse  for  such 
bad  mixtures. 

"  This  is  not  true  of  other  fuels.  Solid  coal  on  a  grate 
is  not  doing  its  best  at  200  ft.,  and  it  takes  a  remarkably 
close  observer  to  note  the  difference  with  a  240-ft.  fire. 
With  oil  this  is  even  more  pronounced.  It  is  the  usual 
thing  to  find  an  oil  fire  with  air  greatly  in  excess,  and  the  fact 
not  known.  The  average  operator  will  not  even  try  to  find 
out  whether  he  is  wrong,  for  in  order  to  do  so  he  must  reduce 
his  air  little  by  little  until  things  go  wrong,  and  that  takes 
time.  Firemen  are  '  not  paid  to  save  fuel/  The  powdered 
coal  fire  begins  to  spark  and  wheeze  when  it  has  too  much 
air.  '  In  a  typical  powdered-coal  feeding  and  burning 
installation,  the  coal  is  received  in  a  bin  over  the  feeders, 


FEEDING  AND  BURNING  POWDERED  COAL          47 


48  POWDERED  COAL  AS  A  FUEL 

where  its  weight  is  about  38  Ib.  per  cubic  foot  when  it  is 
loose  in  the  bin.  Settling  brings  the  weight  down  to  about 
45  Ib.  per  cubic  foot.  Across  the  bottom  of  this  bin,  and 
within  a  pipe  extending  horizontally  from  it,  is  a  double- 
flight  worm  or  feed-screw.  This  double-flight  screw  resists 
the  tendency  of  the  light  coal  to  flow  of  itself  along  the  feed- 
screw. The  screw  extends  over  a  flanged  pipe-cross  into 
which  the  fuel  is  delivered.  The  rear  end  of  the  screw  is 
supported  by  a  bearing  ha  a  flange  on  the  side  of  the  bin, 
the  shaft  projecting  to  receive  a  driving  pulley  or  chain 
sprocket.  The  delivery  end  of  the  screw  shaft  is  supported 
by  a  bearing  in  the  cover  of  the  horizontal  opening  of  the 
flanged  pipe-cross.  The  top  opening  of  the  cross  is  uncovered 
to  permit  air  to  draw  down  with  the  falling  fuel.  This 
fuel  descends  a  vertical  pipe  attached  to  the  lower  opening 
of  the  cross,  the  pipe  being  long  enough  to  be  within  the  fun- 
nel or  injection  pipe.  At  the  bottom  of  the  funnel  is  a  diag- 
onal plate  upon  which  the  fuel  falls.  The  plate  is  tight 
against  the  air  pipe  on  the  up-stream  end,  and  is  flared  open, 
on  the  side  towards  the  furnace  (down  the  current).  It 
covers  about  one-fourth  the  diameter  of  the  pipe,  thus 
forming  at  this  point  a  '  vena  contracta/  and  producing 
a  suction  in  the  funnel.  Consequently,  supplementary  air 
is  drawn  through  with  the  fuel.  The  fuel  spraying  upon  this 
plate  mixes  very  thoroughly  with  the  air  from  the  fan, 
the  eddy  currents  assisting  materially  in  dispersal  of  the 
fuel  through  the  main  column  of  air. 

"  The  admission  funnel  should  be  far  enough  from  the 
furnace  to  permit  this  mixture  to  be  thorough.  Pressures 
carried  abnormally  high  may  defeat  this,  and  they  also 
tend  to  project  the  fuel  too  far  into  the  furnace  before 
flushing.  As  soon  as  the  fuel  cloud  begins  to  absorb  the 
heat  of  the  chamber  into  which  it  passes,  a  rapid  expansion 
of  the  air  takes  place,  separating  the  particles  of  fuel  in 
suspension.  The  amount  of  expansion  is  determined  by  the 
ratio  of  the  absolute  temperatures,  in  the  furnace  and  of  the 
initial  air.  It  is  a  matter  of  discussion  whether  the  best 


FEEDING  AND  BURNING  POWDERED  COAL         49 

results  are  obtained  by  a  delivery  of  all  the  air  found  neces- 
sary for  combustion  through  the  feed  pipe,  or  to  use  a  smaller 
quantity  of  air  in  the  feed  pipe  and  provide  a  further  sup- 
ply from  other  openings.  Good  practice  would  seem  to  point 
to  absolute  control  of  the  air  by  the  fan,  and  control  of  the 
fuel  by  a  varied  speed  of  the  feed-screw.  The  furnace  should 
have  a  good  natural  draft  to  a  chimney,  controlled  by  a 
damper." 

FURNACES 

The  designing  and  building  of  furnaces  is  an  undertaking 
that  calls  for  engineering  skill.  Speeds,  volumes  and  cur- 
rents must  all  be  considered;  sizes  and  areas  influence  heat 
generation  and  distribution;  the  position  of  the  egress 
ports,  if  their  number  or  size  is  great,  may  defeat  the  pur- 
pose of  the  furnace.  It  will  not  do  to  build  a  furnace  in  a 
haphazard  way,  apply  a  burner  somewhere  and,  if  it  does 
not  work,  feed  in  enough  fuel  to  make  it  work.  Perhaps 
there  is  no  fuel  so  sensitive  to  correct  use  as  powdered  coal. 

While  coal  ignites  freely,  in  a  hot  chamber,  this  ignition 
necessitates  the  absorption  of  heat  from  some  source,  and 
if  coal  rapidly  projected  by  air  does  not  develop  its  heat 
near  the  point  of  ignition,  other  means  must  be  devised  to 
maintain  the  heat  necessary  for  ignition  where  ignition  is 
needed,  i.e.,  at  the  first  entrance  of  the  coal  into  the  fur- 
nace. Giving  the  fuel  too  great  velocity  upon  entrance  is 
not  good  practice. 

Some  singular  errors  and  misconceptions  have  attended 
the  practice  of  many  users  of  powdered  coal.  More  par- 
ticularly is  reference  intended  to  the  use  of  large  fans  to 
supply  the  air  necessary  for  the  projection  of  the  fuel, 
where  the  air  nozzle  is  reduced  from  16  or  18  in.  in  diameter 
to  4  or  5  in.  at  the  jet  with  the  expectation  that  all  of  the 
air  in  the  16  or  18-in.  pipe  will  be  hurried  through  the  4  or 
5-in.  nozzle. 

The  first  essential  of  a  powdered  coal  furnace  is  a  large 
combustion  chamber  where  the  flame  can  occupy  about 


50  POWDERED  COAL  AS  A  FUEL 

four  times  the  volume  of  the  flame  produced  by  an  ordinary 
grate  fire.  This  entire  combustion  space  must  be  free  from 
any  metallic  cooling  surfaces.  There  is  little  possibility 
of  such  a  cooling  surface  in  most  metallurgical  furnaces, 
but  this  is  the  probable  reason  why  powdered  coal  has  had 
thus  far  only  limited  application  under  steam  boilers.  Con- 
tact with  a  cooling  surface  stifles  the  flame  and  stops  com- 
bustion. The  reverberatory  type  of  furnace  is  well  suited 
to  the  use  of  powdered  coal.  It  has  a  large  combustion 
space,  which  in  the  case  of  powdered  coal  extends  out  over 
the  hearth.  In  all  cases,  the  fuel  must  be  projected  into  a 
chamber  sufficiently  hot  to  cause  instant  deflagration.  The 
furnace  must  be  properly  proportioned,  properly  equipped 
and  in  good  condition. 

BURNERS 

There  have  been  filed  in  the  United  States  Patent  Office 
almost  as  many  patents  on  powdered  fuel  burners  as  on  non- 
refillable  bottles.  Almost  any  engineer  can  design  a  suc- 
cessful burner  after  knowing  the  requirements.  "  Any 
mechanism  which  will  give  a  uniform  mixture  of  coal  and 
air  with  both  under  control  can  be  used  as  a  burner  for  pow- 
dered coal." 

Burners  are  usually  made  up  of  a  screw  conveyer  of 
variable  speed  which  drops  the  coal  into  a  blast  of  air.  One 
thing  to  be  guarded  against  is  the  possibility  of  flushing. 
Powdered  coal  seeks  its  own  level  like  water.  It  will 
sometimes  run  along  a  screw  conveyer  so  as  to  get  ahead  of 
the  screw.  For  this  reason  the  screw  is  usually  made  very 
long,  so  as  to  introduce  enough  friction  to  keep  back  the 
flush  of  coal. 

There  is  one  very  successful  burner  in  which  no  mechan- 
ism whatever  is  used,  everything  depending  upon  the  blow- 
ing of  air  through  a  pocket  of  powdered  coal.  The  air  picks 
up  enough  of  the  powder  in  its  passage  through  to  provide 
for  combustion.  Possibly  this  apparatus  would  have  a 
closely  limited  capacity. 


FEEDING  AND  BURNING  POWDERED  COAL          51 

Some  of  the  failures  that  have  been  experienced  in  burn- 
ing powdered  coal  have  been  due  to  an  incorrect  method 
of  introduction  of  air  into  the  furnace,  either  by  induced 
draft  or  by  a  blast  separate  from  that  which  supplies  the 
coal.  Air  and  fuel  must  be  mixed  thoroughly  before 
entering.  It  is  possible  to  add  a  little  more  air  after  a 
mixture  has  been  made,  but  good  combustion  should  be  first 
insured  by  a  good  mixture  of  fuel  and  air  at  entrance. 

The  burner  must  be  designed  so  as  to  be  free  from  pockets 
or  storage  spaces,  and  must  be  out  of  the  influence  of  the  heat 
of  the  furnace.  Heat  will  cause  coke  to  form  and  interrupt 
the  operation. 

One  of  the  first  patents  granted  in  connection  with 
powdered  coal  was  that  to  Messrs.  Whelpley  and  Storer  in 
1866.  It  covered  the  simple  operation  of  feeding  powdered 
coal  so  as  to  cause  it  to  come  into  contact  with  the  supply  of 
combustion  air.  The  pulverized  coal  was  to  be  employed 
merely  in  order  to  assist  solid  coal  fires  already  burning  in 
the  furnace.  The  idea  was  that  the  fuel  entering  with  the 
column  of  air  would  meet,  near  the  point  of  entrance,  the 
flames  of  the  furnace  fires.  Thus  as  the  powdered  coal 
entered  the  working  chamber,  it  was  instantly  and  thoroughly 
consumed.  It  was  not  intended  to  dispense  with  the  usual 
fires  maintained  in  the  fire  box  of  the  furnace,  but  merely 
to  augment  them  and  to  economize  in  fuel. 

In  1870,  the  same  inventors  were  granted  a  patent  cover- 
ing a  device  for  introducing  and  regulating  the  supply  of 
powdered  coal  and  air  into  furnaces  and  fire  boxes,  through 
a  large  number  of  openings  (Figs.  12  to  13). 

In  1871,  Mr.  T.  R.  Crampton  was  granted  a  patent  for 
an  improvement  in  apparatus  for  feeding  powdered  coal  to 
furnaces,  which  consisted  of  six,  eight  or  more  or  less  burners 
according  to  the  size  of  the  furnace.  Streams  of  air  mixed 
with  powdered  coal  were  injected  into  the  back  of  the  com- 
bustion chamber  (which  had  a  plain  solid  bottom  without 
fire  bars  or  divisions  of  any  kind)  through  openings  near 
each  other  and  on  the  same  plane,  so  that  the  streams  com- 


52 


POWDERED  COAL  AS  A  FUEL 


mingled  as  they  expanded  on  leaving  their  respective  pipes 
or  openings.  This  assured  uniformity  of  combustion 
superior  to  that  effected  with  either  a  single  pipe  or  with 
branches  from  a  single  pipe  opening  into  the  combustion 
chamber  at  places  too  remote  from  each  other  to  permit 
sufficient  commingling  of  the  fuel  and  air. 


"I 
I     / 
I     ! 


1   i 

!    .  1 1 

i     \    \  \ 


FIG.  12.— Whelpley  &  Storer  Apparatus. 


FIG.  13. — Whelpley  &  Storer  Apparatus. 

In  order  still  further  to  promote  combustion,  the  bridge 
wall  was  constructed  with  a  suitable  slope  towards  the  open- 
ings, so  that  the  commingled  streams  impinging  on  it  at  an 
angle  spread  in  all  directions.  This  led  to  a  further  com- 
mingling; and  a  combination  of  air  and  fuel  homogeneous 


FEEDING  AND  BURNING  POWDERED  COAL          53 

in  its  character  was  deflected  over  the  bridge  wall  ready  to 
do  its  work  in  the  furnace. 

Instead  of  relying  upon  the  combination  of  air  and  fuel 
escaping  from  a  single  pipe  as  sufficiently  perfect  to  secure 
continuous  and  uniform  combustion,  the  fuel  and  air  were 
thus  subjected  to,  first,  the  action  of  similar  streams  from 
adjacent  pipes;  and,  second,  impingement  upon  the  bridge 
wall,  or  even  upon  the  bottom  of  the  combustion  chamber. 
The  powdered  coal,  ground  to  the  required  fineness,  was 
placed  in  rectangular  reservoir,  located  above  the  plane  of 
the  pipes.  In  this  reservoir  there  were  rotating  stirrers 
which  urged  the  fuel  through  a  gate  at  one  end  of  the  reser- 
voir, and  upon  a  roller,  a  part  of  whose  periphery  formed 
the  bottom  of  a  box  attached  to  the  reservoir  which  sup- 
ported the  fuel  issuing  from  the  gate. 

Above  the  roller,  just  described,  was  another  and  smaller 
one,  a  part  of  whose  periphery  was  within  the  box;  the  two 
rollers  by  proper  gearing  being  made  to  move  at  about  the 
same  surface  speed. 

The  rollers  were  adjustable  as  to  speed,  and  received 
between  their  faces  the  powdered  coal  passing  through  the 
gate  of  the  reservoir.  They  delivered  it  in  a  thin  sheet  of 
grains  of  uniform  size  into  a  trough,  from  which  descended 
as  many  receiving  tubes  as  there  were  conducting  tubes 
leading  to  the  furnace. 

The  upper  openings  of  the  receiving  tubes  in  the  trough 
were  rectangular,  and  so  arranged  side  by  side  as  to  divide 
equally  the  sheet  of  grains  falling  into  them  into  as  many  por- 
tions as  there  were  conducting  tubes. 

The  bottoms  of  the  receiving  tubes  were  circular,  and 
they  were  united  each  to  its  separate  conducting  tube, 
slightly  on  the  furnace  side  of  the  open  end  of  the  latter. 

Having  thus  secured  to  each  conducting  tube  an  equal 
supply  of  fuel,  the  next  thing  to  be  done  was  to  combine 
or  mix  this  fuel  with  air,  and  to  force  the  combination,  then 
called  "  carbonized  air,"  into  the  combustion  chamber. 
This  was  effected  by  a  fan  or  similar  contrivance.  The 


54  POWDERED  COAL  AS  A  FUEL 

blast  of  air  was  forced  into  a  cylinder  in  the  same  plane 
with  the  conducting  tubes,  opposite  to  the  open  ends  of 
which  were  an  equal  number  of  air  nozzles. 

These  nozzles  were  smaller  in  diameter  than  the  open 
ends  of  their  respective  tubes,  and  at  a  short  distance  there- 
from, so  that  there  was  space  into  which  the  external  air 
might  enter  into  the  conducting  tubes  along  with  that  which 
was  forced  into  them  from  the  air  nozzles  (Figs.  14  and  15). 

In  1871  a  patent  was  granted  to  Mr.  J.  Y.  Smith  of 
Pittsburgh,  Pa.,  on  a  device  shown  in  Figs.  16  to  18,  which 
the  inventor  describes  as  follows: 

"  An  apparatus  for  feeding  powdered  coal  into  a  furnace, 
combining  in  its  construction  the  following  elements,  viz., 
an  induction  and  an  exhaust  pipe,  an  intermediate  wheel 
arranged  to  be  revolved  by  the  action  of  a  current  of  steam, 
air  or  gas  passing  through  said  pipe,  and  a  shoe  or  other 
f eeding  mechanism  regulating  the  discharge  of  the  powdered 
coal  connected  with  said  wheel/' 

In  combination  with  a  pipe  or  series  of  pipes  for  passing 
a  current  of  steam  or  gas  into  the  furnace  or  combustion 
chamber,  there  is  employed  a  hopper  or  pipe  for  delivering 
into  such  current,  the  powdered  coal;  and  an  opening  or 
series  of  openings  for  introducing  air  mingled  with  the 
steam  or  gas  and  powdered  coal  into  the  furnace  or  combus- 
tion chamber. 

In  1876  Mr.  Wm.  West  of  Golden  City,  Col.,  was  granted 
a  patent  for  a  powdered  coal  burner  which  consisted  of  a 
small  screw  conveyer  for  feeding  the  coal  dust  from  a  bin 
to  one  or  more  tubes;  from  which  it  dropped  through  a 
funnel-shaped  pipe  into  a  blast  pipe.  From  this,  the  air 
picked  it  up  and  carried  it  into  the  furnace.  The  screw  had 
a  cone  pulley  or  other  means  for  regulating  the  speed  of  the 
conveyer  (Fig.  19  to  20). 

In  1880  Mr.  West  together  with  Mr.  John  G.  McAuley 
improved  the  design  of  this  powdered  coal  feeder  and  were 
granted  a  patent  on  their  improvement.  It  consisted  of 
constructing  the  feeder  with  a  vertical  conduit,  through 


FEEDING  AND  BURNING  POWDERED  COAL          55 


56 


POWDERED  COAL  AS  A  FUEL 


FIG.  16. — Smith  Burner  and  Feeder. 


FIG.  17. — Smith  Burner  and  Feeder. 


TCI- 


FIG.  18. — Smith  Burner  and  Feeder. 


FEEDING  AND  BURNING  POWDERED  COAL          57 

which  the  powdered  coal  dropped,  communicating  with  a 
horizontal  pipe  which  was  made  of  greater  inside  diameter 


H 


FIG.  19.— West  Feeder. 


FIG.  20. — West  Feeder. 

just  back  of  the  point  of  entrance  of  the  coal  than  it  was 
farther  back.  An  inclined  shelf,  at  the  bottom  of  the  verti- 
cal fuel  conduit,  prevented  the  blast  of  air  from  striking 


58  POWDERED  COAL  AS  A  FUEL 

upward  and  made  for  a  better  mixing  of  the  particles  of  coal 
dust  and  air. 

The  Edison  patents  on  feeding  and  burning  equipment 
are  described  in  Chapter  V.  Other  apparatus  of  this  sort 
will  be  found  discussed  in  Chapters  VIII  and  IX. 

Pneumatic  Feeding  System.  In  most  plants  using  pow- 
dered coal  the  above-described  screw  conveyer  system  is 
employed.  About  a  year  ago  the  author  visited  a  number 
of  works  using  powdered  coal.  Among  them  were  several 
that  are  using  the  air  distributing  (Holbeck)  system;  and 
the  contrast  between  the  two  systems  was  most  marked. 

The  air  distributing  system  is  briefly  described  as  fol- 
lows :  Air  is  the  agent  used  for  conveying  the  coal  dust  to  the 
furnaces.  The  coal  is  first  pulverized  in  the  usual  manner 
and  delivered  to  a  storage  bin  located  in  the  coal  building. 
This  bin  is  the  only  one  used  for  storing  powdered  coal  in 
the  entire  plant.  It  is  made  of  sufficient  capacity  to  serve 
the  furnaces  for  ten  hours. 

The  powdered  coal  is  taken  from  this  bin  by  a  standard 
double-flight  screw  conveyer,  driven  by  a  variable  speed 
motor:  and  is  then  fed  into  the  suction  side  of  a  high- 
pressure  blower.  From  this  it  is  blown  into  the  distributing 
main  and  carried  to  the  furnaces  through  branch  pipes. 
The  coal  which  is  not  used  at  the  furnaces  is  returned  through 
a  return  line  to  a  collector  located  on  top  of  the  powdered 
coal  bin,  where  it  is  extracted  from  the  air  and  falls  hi  to 
the  storage  bin  to  be  fed  over  again.  The  air  from  the  return 
line,  after  the  coal  is  extracted,  is  returned  to  the  suction 
side  of  the  distributing  blower. 

Interposed  in  the  distributing  main  is  a  special  flow 
indicator  and  controller;  intended,  first,  to  indicate  the 
rate  of  flow  of  air  through  the  system  and  second,  to  con- 
trol the  feed  of  powdered  coal  into  the  system  so  as  to  have 
a  uniform  mixture  of  coal  dust  and  air  to  the  burners, 
regardless  of  the  number  of  furnaces  in  operation. 

The  return  line  permits  a  velocity  of  air  in  the  distribut- 
ing main  sufficiently  high  to  keep  the  powdered  coal  in  sus- 


FEEDING  AND  BURNING  POWDERED  COAL          59 

pension  of  the  air  and  in  circulation  in  the  system,  even 
with  no  furnaces  in  operation. 

When  the  valves  in  the  branches  at  the  furnaces  are 
opened  so  as  to  permit  a  flow  of  coal  dust  to  the  burners, 
there  is  an  increase  in  the  flow  of  air  through  the  flow 
indicator.  This  increased  flow  is  instantly  indicated  on  the 
indicator  dial  as  shown  in  Fig.  21.  At  the  same  time 
a  small  pilot  motor  is  started,  and  by  means  of  proper 
gearing  the  arm  of  a  special  field  rheostat  is  moved  in  pro- 
portion to  the  increase  in  the  flow  of  air  through  the  dis- 
tributing mains.  This  rheostat  controls  the  variable  speed 
motor  that  drives  the  feed  screw,  thus  speeding  up  this 
motor  and  feeding  more  coal  dust  to  meet  the  demand. 
In  case  a  valve  of  the  furnace  should  be  partly  closed,  thus 
causing  a  decrease  in  the  flow  of  air  through  the  system, 
the  pilot  motor  is  automatically  reversed,  the  rheostat 
arm  is  moved  in  the  opposite  direction,  and  the  motor  driv- 
ing the  feed-screw  is  slowed  down  so  that  the  mixture  of 
coal  dust  and  air  is  automatically  kept  uniform. 

With  this  system,  the  powdered  coal  can  be  conveyed 
to  any  reasonable  distance.  The  author  has  seen  a  plant 
where  the  first  furnace  was  400  ft.  from  the  pulverizing 
plant,  and  another  where  the  last  furnace  on  the  line  was 
1500  ft.  from  the  milling  plant.  If  the  velocity  of  flow 
is  reduced,  due  to  friction  in  the  main,  a  second  or  even  a 
third  and  fourth  distributing  blower  or  booster  can  be 
placed  in  the  line  and  thus  the  circulation  can  be  kept  up 
for  an  indefinite  distance. 

The  advantage  of  handling  the  coal  dust  in  this  way 
over  the  old  system  of  using  screw  conveyors,  are: 

1.  When  it  is  taken  into  consideration  that  the  air  used 
for  conveying  the  coal  dust  is  also  used  to  take  the  place  of 
the  secondary  air  for  combustion,  that  would  have  to  be 
furnished  by  some  other  means,  the  actual  consumption 
of  power  for  furnishing  coal  dust  to  the  furnaces  is  very  low. 

2.  The  wear  and  high  cost  of  repairs  incidental  to  the  old 
method  of  using  screw  conveyers  is  eliminated.     It  is  esti- 


60 


POWDERED  COAL  AS  A  FUEL 


mated  that  a  9-in.  screw  conveyer  costs  about  $4.50  per 
lineal  foot  and  the  power  cost  to  turn  it  will  average  at  least 


d3Zld3Aind 

$1.00  per  day  for  every  run  of  250  ft.  Screw  conveyers 
are  apt  to  clog  up  and  stop  feeding,  necessitating  work  to 
locate  the  stoppage  and  then  to  make  repairs. 


FEEDING  AND  BURNING  POWDERED  COAL          61 

3.  Air  distribution  entirely  eliminates  the  storage  bin 
at  each  individual  furnace,  which  takes  up  a  great  deal  of 
space  that  can  be  used  for  other  purposes.     It  also  eliminates 
the  "  hanging-up  "  of  coal  dust  at  the  furnaces,  which  may 
cause  avalanching  and  flushing  past  the  controllers,  leading 
the  furnaces  to  puff  or  smothering  the  fire.     This  difficulty 
from  powdered  coal  (caking  at  the  bins)  seems  to  be  quite 
general.     The  writer  has  seen  the  coal  dust  bins  suspended 
by  springs  in  shops  where  it  was  endeavored  to  stop  the 
caking  of  the  coal  resulting  from  the  jarring  of  forge  ham- 
mers. 

4.  Within  a  few  minutes  after  the  furnaces  are  shut  off, 
all  of  the  coal  dust  in  the  distributing  system  is  returned 
to  the  pulverized  coal  plant,  thus  leaving  no  coal  dust  in 
storage  in  the  works  or  at  the  furnaces. 

With  this  system  of  distribution,  there  is  no  large  com- 
bustion chamber  built,  nor  is  the  existing  furnace  changed 
to  any  extent.  The  oil  or  gas  supply  is  cut  off  and  one  or 
two  small  branches  of  pipe  are  brought  down  to  the  furnace 
with  a  valve  near  the  main,  fixed  so  that  it  can  be  operated 
from  the  floor. 

The  distributing  main  consists  of  spiral  riveted  pipe 
running  overhead  and  feeding  the  furnaces.  If  there  are 
ten  or  twelve  furnaces,  and  it  is  desired  to  shut  down  one 
or  more  of  them,  the  valves  at  the  branches  are  closed  and 
the  automatic  controller  does  the  rest. 

For  getting  rid  of  ash  and  smoke,  the  front  side  walls  of 
the  furnaces  are  built  out  and  a  sheet  steel  hood  is  placed 
directly  across  the  front  of  each  furnace,  the  bottom  of  the 
hood  resting  just  above  the  work  opening;  each  hood  is 
tapered  into  a  small  pipe  and  connected  to  an  exhaust 
main.  At  one  end  of  the  shop  an  exhauster  is  placed  to 
which  this  exhaust  main  is  connected  and  the  contents  are 
discharged  into  a  separator  placed  outside  of  the  building. 
Underneath  the  separator  is  a  storage  bin,  from  which  the 
ash  can  be  removed. 


CHAPTER  V 
POWDERED  COAL  IN  THE  CEMENT  INDUSTRY 

AMONG  the  various  applications  of  powdered  coal, 
the  first  was  in  the  manufacture  of  cement. 

About  forty-three  years  ago,  Mr.  William  Sweet  of  Dil- 
worth,  Porter  &  Company,  was  using  powdered  coal,  em- 
ploying a  screw  and  fan  to  inject  the  coal  into  the  furnaces. 
The  coal  was  simply  crushed  as  fine  as  it  could  be  between 
ordinary  rolls  and  this  lack  of  the  fineness  required  for 
burning  probably  accounted  for  the  failure  of  the  project. 

For  the  past  thirty  years  there  have  been  suggested  many 
schemes  for  burning  powdered  coal  in  cement  plants,  under 
boilers  and  in  heating  furnaces.  A  large  number  of  burners 
and  processes  have  been  introduced  with  varying  degrees 
of  success. 

During  the  early  years  of  the  cement  industry  in  this 
country,  oil  was  employed  as  a  fuel  by  spraying  it  into  the 
lower  end  of  the  furnace  with  a  jet  of  compressed  air  or 
steam.  The  use  of  oil  was  successful,  but  due  to  the  in- 
creasing cost  after  1895,  very  expensive.  From  1897  to 
1900  the  increase  in  price  was  so  great  as  to  make  the 
use  of  oil  almost  impracticable  commercially.  This  fact 
has  been  the  principal  incentive  for  developing  the  use  of 
powdered  coal. 

In  1894  a  series  of  experiments  on  the  use  of  powdered 
coal  was  begun  by  the  Atlas  Portland  Cement  Company. 
These  were  in  immediate  charge  of  Messrs.  Hurry  and 
Seaman,  Chief  Engineer  and  Superintendent  respectively. 
They  led  to  many  discoveries,  the  invention  of  various  devices 
and  finally  to  the  commercial  development  of  the  art. 
Hurry  and  Seaman  are  entitled  to  the  credit  of  having  been 
the  first  successful  users  of  powdered  coal  in  the  cement  in- 

62 


POWDERED  COAL  IN  THE  CEMENT  INDUSTRY      63 

dustry.  This  use  was  begun  in  1895  by  the  Atlas  Company 
and  has  never  been  discontinued.  Other  engineers  working 
along  independent  lines  attained  success  a  few  years  later. 
Possibly  they  received  some  assistance  from  information  dis- 
seminated throughout  the  industry  relating  to  the  results 
obtained  by  Hurry  and  Seaman.  At  the  particular  date 
referred  to,  every  mill  in  the  industry  jealously  guarded 
information  regarding  details  of  manufacture  as  valuable 
trade  secrets.  Consequently,  little  or  no  direct  information 
as  to  details  of  processes  or  machinery  employed  was  com- 
mon in  the  different  mills.  The  information  which  leaked 
out  was  generally  inaccurate  and  inferences  were  based 
on  speculation  or  rumors.  The  success  of  the  process  of 
burning  powdered  coal  in  the  Atlas  plant  was  not  generally 
realized  until  about  1900,  when  the  process  was  put  in  opera- 
tion in  various  other  plants  by  independent  investigators. 

Portland  cement  is  manufactured  from  a  mixture  of 
materials  containing  lime  and  silica,  which  are  brought 
together  in  definite  proportions  and  caused  to  unite  in  chem- 
ical combination.  The  raw  material  is  principally  carbonate 
of  lime,  or  limestone  in  some  form,  with  clay  or  shale.  The 
materials  are  pulverized  raw  and  mixed,  either  in  the  form 
of  a  dry  powder  or  ha  a  wet  condition.  They  are  then 
delivered  to  the  kiln,  where  they  are  subjected  to  an  ex- 
tremely high  temperature,  at  which  the  required  chemical 
combinations  take  place.  In  the  early  days  of  the  art, 
fixed  kilns  were  employed,  but  at  the  present  tune  the  rotary 
kiln  is  almost  universally  used. 

According  to  Prof.  R.  C.  Carpenter  (Trans.  A.S.M.E., 
Vol.  36),  the  rotary  kiln  in  its  essential  features  was  patented 
by  Siemens  in  1869,  and  in  combination  with  a  gas  burner 
and  other  appliances,  by  Ransome  in  1885.  It  was  not  found 
successful  for  cement  burning  in  England,  but  was  improved 
and  developed  in  the  United  States  by  the  Atlas  Company 
about  1890,  and  by  other  American  companies,  to  such  a 
degree  that  it  displaced  practically  every  other  method  of 
burning  Portland  cement. 


64  POWDERED   COAL  AS  A  FUEL 

"  The  modern  rotary  cement  kiln  consists  of  a  slightly 
inclined  steel  cylinder  mounted  on  steel  rollers  and  arranged 
so  that  it  can  be  revolved.  The  upper  end  is  connected 
with  a  stack  or  chimney  which  permits  of  the  escape  of  dis- 
charge gases.  The  raw  cement  material,  in  the  form  of  dust 
or  '  slurry/  enters  the  upper  end  of  the  kiln.  At  the  lower 
end  of  the  cylinder  is  a  stationary  hood  which  affords  a  dis- 
charge opening  for  the  burned  material  and  which  also  acts 
as  a  support  for  the  fuel-supplying  devices.  The  rotary  cylin- 
ders are  of  various  dimensions.  The  tendency  has  been  con- 
tinually to  increase  the  size  of  cylinder.  Thus,  for  instance, 
in  1890  the  rotary  kilns  were  in  some  instances  4  ft.  in 
external  diameter  and  40  ft.  in  length.  From  1895  to  1902 
kiln  dimensions  were  quite  generally  6  ft.  in  diameter  and 
60  ft.  long.  At  the  present  time  kilns  10  ft.  in  diameter  and 
150  to  200  ft.  long  are  common.  The  Atlas  plant  at  Hudson 
is  equipped  with  kilns  12  ft.  in  diameter  and  275  ft.  long.  In 
most  of  the  late  installations  the  kilns  are  true  cylinders 
having  the  same  diameter  at  each  end;  but  in  many  plants 
kilns  are  to  be  found  with  the  diameter  at  the  top  about 
1  ft.  less  than  that  at  the  bottom,  the  two  parts  being 
connected  by  a  tapered  section  forming  the  frustum  of  a 
cone. 

"  The  rotary  kiln  is  lined  throughout  with  a  fire-brick 
lining,  except  in  rare  cases  where  a  very  wet  slurry  is  em- 
ployed, in  which  case  the  lining  for  a  short  distance  from  the 
upper  end  is  omitted.  The  temperatures  in  the  combus- 
tion chamber  required  for  burning  cement  clinker  are  from 
2800  to  3000°  F.  To  withstand  these  high  temperatures  a 
lining  having  high  refractory  qualities  must  be  employed. 
It  must  also  have  the  quality  of  withstanding  decomposi- 
tion by  the  chemical  action  taking  place  in  the  kiln.  The 
problem  of  kiln  linings  has  been  a  serious  one.  The  lower 
part  especially  has  to  be  repaired  frequently  unless  condi- 
tions are  unusually  favorable." 

The  kiln  is  so  operated  as  to  keep  the  lining  coated  with 
the  cement  mixture  for  the  purpose  of  protection. 


POWDERED  COAL  IN  THE  CEMENT  INDUSTRY      65 


66 


POWDERED  COAL  AS  A  FUEL 


Fig.  22  shows  the  general  features  and  arrangement  of 
the  various  operating  parts  of  a  typical  rotary  cement  kiln. 
In  this  illustration  the  kiln  is  shown  at  C,  the  flue  for  dis- 
charge gases  at  B,  the  supporting  rolls  at  D-D,  the  sta- 
tionary hood  at  the  lower  end  at  E,  the  rotary  clinker  cooler 
at  6r,  the  clinker  pit  at  F,  the  blower  for  supplying  compressed 
air  at  H,  the  coal  bin  at  K,  the  feeding  injector  for  coal 
dust  at  J,  the  conveyer  for  delivering  coal  to  the  fuel  tank 


FIG.  23. — Injector  for  Cement  Kiln. 

at  L,  and  the  dust  bin  for  raw  material  at  A.  The  hood,  E, 
is  usually  mounted  on  rolls  so  as  to  be  easily  moved  away 
when  repairing  the  kiln.  It  is  customary  to  supply  a  sepa- 
rate stack  for  each  kiln,  although  in  some  cases  one  stack 
received  the  discharge  from  two  kilns.  In  a  large  instal- 
lation it  is  customary  to  supply  the  air  for  several  burners 
from  one  blower.  In  the  installation  shown,  the  blower 
draws  in  air  which  has  first  been  warmed  by  passing  through 
a  rotary  clinker  cooler. 

Fig.  23  gives  an  idea  of  the  character  of  the  combustion 
which  takes  place  in  the  burning  of  powdered  coal  in  a 
cement  kiln.  The  powdered  coal  is  delivered  to  the  kiln 
by  a  jet  of  air  which  impinges  on  the  fuel  dust  with  force 
enough  to  discharge  the  dust  into  the  kiln.  The  compressed 


POWDERED   COAL  IN  THE  CEMENT  INDUSTRY      67 


68  POWDERED  COAL  AS  A  FUEL 

air  may  be  obtained  from  a  fan  or  a  compressor,  as  may  be 
convenient;   the  illustration  shows  both  schemes. 

The  injector  varies  greatly  in  different  constructions,  but 
in  all  cases  it  performs  the  function  of  injecting  the  coal 
dust  into  the  kiln  by  a  jet  of  air.  It  always  consumes  less 
than  the  amount  needed  for  combustion.  The  additional 
air  needed  for  combustion  enters  the  kiln  principally  through 
openings  in  the  hood  and  through  the  discharge  duct  for 
clinker.  Such  openings  are  shown  in  Fig.  23  by  arrows 
at  points  marked  a.  The  amount  of  air  supplied  by  the 
compressors  or  fans  should  be  sufficient  merely  to  carry  the 
dust  into  the  kiln  without  producing  a  combustible  or 
explosive  mixture.  The  fuel  dust  enters  the  combustion 
chamber  of  the  kiln  in  the  form  of  a  black  cloud  and  burns 
like  an  elongated  torch,  as  indicated  in  Fig.  24.  The  length 
of  the  flame  in  actual  kiln  constructions  is  generally  from 
25  to  40  ft.,  although  this  is  affected  by  local  conditions. 
The  diameter  of  the  flame  in  some  places  may  be  very  nearly 
equal  to  that  of  the  combustion  chamber.  Under  the  best 
conditions  of  burning  the  flame  does  not  perceptibly  im- 
pinge against  the  side  walls  of  the  kiln,  and  the  heat  utilized 
is  practically  all  given  off  by  radiation. 

EDISON   SYSTEM 

In  1904,  Mr.  Thomas  A.  Edison  designed  and  patented 
a  method  of  burning  Portland  cement  clinker  by  the  use 
of  powdered  coal,  which  is  described  as  follows: 

The  invention  consists  in  a  method  whereby  a  greater 
amount  of  fuel  may  be  consumed  in  kiln  cylinders  without 
raising  the  temperature  to  which  they  are  now  usually 
subjected.  Thus  the  desired  quality  of  material  is  secured, 
while  the  output  thereof  is  largely  increased. 

"  The  rotary  cylinder  burners  heretofore  in  common  use 
for  burning  Portland  cement  materials  consist  of  a  cylinder 
about  60  ft.  in  length  lined  with  fire  brick  and  having  an 
inside  diameter  of  from  4  to  5  ft.,  the  cylinder  being  set  at 
a  slight  angle  and  the  powdered  coal  being  fed  in  at  the  upper 


POWDERED  COAL  IN  THE  CEMENT  INDUSTRY      69 


FIG.  25. — Edison  System. 


FIG.  26.— Edison  System. 


70  POWDERED  COAL  AS  A  FUEL 

end  thereof.  The  rotation  of  the  cylinder,  by  reason  of  its 
inclination,  slowly  advances  the  material  toward  and  out 
of  the  lower  end.  The  speed  of  progression  of  the  material 
lengthwise  through  the  cylinder  depends  upon  the  speed  of 
rotation  and  the  inclination  of  the  cylinder.  The  exit 
or  lower  end  of  the  cylinder  opens  into  a  closed  chamber 
provided  with  an  orifice  at  the  bottom  through  which  the 
burned  material  may  make  its  exit. 

"  With  such  cylindrical  kilns  as  have  heretofore  been 
used,  there  is  inserted  in  this  chamber,  in  an  axial  line 
with  the  bore  of  the  cylinder,  a  nozzle,  through  which 
(by  means  of  compressed  air)  a  stream  of  powdered  coal  is 
projected  into  the  cylinder  and  there  consumed.  Total 
combustion  of  the  powdered  coal  takes  place  within  a  rela- 
tively limited  distance  near  the  lower  end  of  the  cylinder, 
such  distance  being  perhaps  not  over  20  ft.  The  very  high 
temperature  necessary  for  the  final  clinkering  of  the  cement 
materials  is  restricted,  however,  to  a  much  smaller  distance 
—say  about  8  ft.  of  the  length  of  the  cylinder.  With 
cylinders  of  the  dimensions  indicated,  and  providing  for 
total  combustion  of  the  powdered  coal  in  approximately 
the  distance  mentioned,  about  2800  Ib.  of  cement  clinker 
are  produced  per  hour  with  an  expenditure  of  about  800  Ib. 
of  coal  dust,  the  maximum  temperature  reached  being 
approximately  3000°  F.  The  gases  of  combustion  are  swept 
forward  in  the  cylinder  and  impart  their  heat  to  the  advanc- 
ing material,  finally  finding  their  exit  through  a  stack  at 
the  feed  end  at  which  the  cold  material  is  introduced.  The 
compressed  air  for  projecting  the  powdered  coal  through  the 
nozzle  into  the  cylinder  being  insufficient  to  effect  its 
complete  combustion,  the  additional  air  necessary  for  that 
purpose  is  introduced  through  the  exit  orifice  for  the 
burned  clinker.  This  supplementary  air  is  drawn  in  by 
reason  of  the  draft  created  by  the  stack  and  by  the  com- 
pressed air.  The  small  amount  of  material  which  passes 
through  the  cylinder  has  so  limited  a  capacity  for  the 
absorption  of  heat  when  it  enters  the  contracted  zone  of 


POWDERED  COAL  IN  THE  CEMENT  INDUSTRY       71 

high  temperature  that  it  effects  very  little  lowering  of 
temperature.  In  practice  it  is  necessary  that  the  tempera- 
ture in  the  contracted  zone,  or  in  the  zone  of  effective 
clinkering,  should  not  vary  except  within  narrow  limits. 
If  the  temperature  is  too  low  the  chemical  reaction  neces- 
sary to  form  good  cement  does  not  take  place,  or  only 
partially  so;  while  on  the  other  hand  if  the  temperature  is 
too  high  the  clinker  will  be  nearly  melted,  and  when  thus 
over-burned,  undesirable  chemical  reactions  take  place, 
making  an  improper  cement.  If  with  the  proper  propor- 
tions of  coal  and  air,  adjusted  to  produce  the  desired 
clinkering  temperature,  the  amount  of  material  fed  into 
the  cylinder  is  doubled,  with  a  corresponding  increase 
in  the  amount  of  fuel  and  air,  then  twice  as  much  coal  will 
be  burned  in  substantially  the  same  distance,  and  the 
temperature  will  therefore  rise  to  so  great  an  extent  that  the 
material  will  be  over-burned  and  the  fire  brick  lining  of  the 
cylinder  will  suffer  injury.  The  additional  amount  of 
material  fed  will  not  be  sufficient  materially  to  lower  the 
temperature  in  the  clinkering  zone,  and  hence  with  usual 
cylinders  as  now  arranged  and  operated  the  output  is 
nearly  fixed  and  cannot  be  exceeded." 

The  Edison  invention  covers  a  method  by  which  the 
output  of  material,  with  burners  of  the  type  described,  can 
be  very  greatly  increased.  This  is  accomplished  by  alter- 
ing the  conditions  of  combustion  and  extending  the  area 
of  high  temperature,  i.e.,  the  clinkering  zone,  over  a  greater 
length  of  the  cylinder.  The  kiln  is  thus  enabled  to  burn 
a  very  much  greater  amount  of  fuel,  and  carry  through 
the  cylinder  and  properly  burn  a  very  much  greater  amount 
of  cement  or  other  material,  without  raising  the  temperature 
in  any  part  of  the  zone  of  maximum  heat  above  that  required 
to  secure  proper  results.  To  this  end  there  are  employed 
two  or  more  combustion  zones  within  the  cylinder,  each  pro- 
viding for  a  zone  of  clinkering  heat.  The  point  of  maxi- 
mum temperature  of  one  zone  is  preferably  made  closely 
adjacent  to  the  point  of  maximum  temperature  of  the  second 


72  POWDERED  COAL  AS  A  FUEL 

zone,  so  as  to  secure  anywhere  between  such  points  a  suf- 
ficiently high  temperature  to  obtain  the  desired  clinkering 
effect. 

In  this  way  it  is  possible  to  secure  within  the  burner  a 
much  larger  proportional  area  of  effective  combustion  with 
relation  to  the  quantity  of  fuel  used  than  is  now  possible. 

To  illustrate  the  principle  generally,  assume  two  nozzles 
to  be  employed,  one  being  supplied  with  powdered  coal  and 
air  at  say,  50  Ib.  pressure  per  square  inch,  which  serves  to 
throw  the  fuel  with  great  velocity  into  the  cylinder,  so 
that  the  center  of  its  zone  of  combustion  is  say,  25  ft.  from 
the  exit  end  of  the  cylinder:  and  the  other  being  supplied 
with  coal  and  air  at  say,  20  Ib.  pressure,  so  that  the  zone  of 
combustion  thereof  will  be  located  between  the  first  zone 
and  the  exit  end.  The  columns  of  air  and  powdered  coal 
from  the  nozzles,  on  account  of  their  great  velocity,  pass  into 
the  cylinder  for  a  considerable  distance  before  spreading 
and  before  the  temperature  of  either  reaches  the  com- 
bustion point.  By  employing  a  number  of  nozzles,  sup- 
plied with  air  at  different  pressures,  and  with  the  proper 
amount  of  coal  fed  into  each,  a  very  large  amount  of  coal 
can  be  burned;  and  the  extent  of  the  zone  of  clinkering 
temperature  may  be  increased.  Thus  the  output  of  finished 
material  may  be  largely  augmented.  In  this  way  a  con- 
siderable saving  is  secured  in  investment  and  operating 
labor  per  ton  of  output;  while  an  additional  saving  is  secured 
hi  the  dimunition  of  the  amount  of  coal  necessary  to  burn  a 
given  amount  of  material,  because  of  the  diminished  loss  by 
external  radiation. 

In  other  words,  by  directing  the  different  columns  or 
streams  of  powdered  coal  within  the  cylinder  so  that  the 
areas  of  combustion  will,  so  to  speak,  "  overlap,"  it  is  pos- 
sible to  secure  an  additional  area  of  clinkering  temperature 
or  an  additional  zone  of  high  heat;  which  cannot  be  secured 
with  a  single  burning  column  of  fuel  or  with  a  plurality  of 
such  columns  of  fuel  separated  to  too  great  an  extent. 


POWDERED  COAL  IN  THE  CEMENT  INDUSTRY      73 


KILN   CALCULATIONS 


Adequate  drying  of  the  coal  is  generally  considered 
essential,  although  for  some  small  plants  the  writer  has  seen 
kilns  in  operation  on  coal  which  had  not  been  dried.  Wet 
coal  has  a  detrimental  effect  on  feeding  and  on  the  capacity 
of  the  kiln.  The  effect  of  the  moisture,  however,  depends 
upon  the  kind  of  coal,  so  that  no  limit  can  be  definitely 
stated  as  essential  to  success  in  advance  of  a  trial. 

According  to  Carpenter,  the  weight  of  powdered  coal 
required  per  barrel  of  cement  varies  somewhat  with  the 
character  of  the  kiln  and  the  character  of  the  process.  In 
the  dry  process  of  manufacture,  the  weight  of  coal  is  from 
83  to  100  Ib.  per  barrel  of  cement.  In  the  wet  process  the 
coal  varies  from  about  35  to  50  per  cent  of  the  finished 
product,  that  is,  from  133  to  190  Ib.  of  coal  per  barrel. 
The  theoretical  amount  of  coal  required  disregarding  the 
heat  due  to  the  formation  of  silicates  of  lime  and  alumina, 
is  probably  not  far  from  30  Ib.  per  barrel,  provided  10,000 
B.t.u.  per  pound  of  coal  are  utilized.  Continuous  stationary 
kilns  are  reported  as  consuming  12  to  16  per  cent  of  fuel 
of  from  45  to  60  per  barrel  of  cement. 

"  The  capacity  of  the  modern  kiln  in  barrels  per  twenty- 
four  hours  when  operating  on  dry  material  with  flue  gases 
at  about  1000°  F.  may  be  approximately  expressed  by  the 
following  formula: 


where  C  =  capacity  in  24  hours,  in  barrels  of  380  Ib.; 
D  =  outside  diameter  in  feet; 
L=  length  in  feet. 

"  The  economy  of  the  kiln  has  been  increased  by  in- 
creasing  its  length.  This  is  due  in  part  to  a  change  in  proc- 
ess of  burning:  the  CO  being  driven  off  from  the  material 
before  it  reaches  the  combustion  zone  in  the  kiln:  and  in 


74  POWDERED  COAL  AS  A  FUEL 

part  to  a  reduction  of  losses.  The  saving  due  to  the  use  of  a 
150-ft.  kiln  in  place  of  a  60-ft.  kiln  has  exceeded  20  per  cent 
in  fuel,  and  in  addition  has  cut  down  the  labor  required 
in  operation  more  than  one-half.  Kilns  can  be  operated 
with  a  stack  temperature  of  less  than  1000°  F.,  but  in  such 
event  the  capacity  is  lessened  and  the  result  is  generally  an 
increase  rather  than  a  decrease  in  cost. 

"  Mr.  Richard  K.  Meade,  in  his  book  on  Portland  cement, 
gives  the  following  calculation  as  to  the  heat  necessary 
per  100  Ib.  of  raw  material: 

Heat  required:  B.t.u. 

Decomposition  of  75  Ib.  CaCO     75X784  =58,800 
Decomposition  of  4  Ib.  MgCO       4X384  =  1,536 


60,336 

Heat  supplied : 

Burning  of  0.3  Ib.  sulphur     0.3  X  4,050   =  1,215 
Burning  of  0.8  Ib.  carbon      0.8  X  14,540   =11,632 


12,847 

Balance  to  be  supplied  by  fuel:    60,336 

12,847 


47,489  B.t.u. 

"  About  600  Ib.  of  raw  material  are  needed  per  barrel, 
so  that  the  total  heat  required  per  barrel  would  be  284,934 
B.t.u.,  disregarding  the  effect  of  the  silicates.  The  combi- 
nation of  the  silicates  and  lime  gives  off  heat.  The  amount 
is  in  doubt  as  the  exact  resulting  composition  of  the  silicates 
is  not  known.  A  certain  combination  might  produce 
44,700  B.t.u.  per  100  Ib.  of  raw  material;  this  is  hardly 
possible  as  it  would  reduce  the  heat  to  be  supplied  to  2789 
B.t.u.  per  100  Ib.  of  raw  material  or  to  16,734  B.t.u.  per  barrel 
of  cement.  At  47,489  B.t.u.,  with  coal  evolving  10,000 
B.t.u.,  the  weight  of  coal  per  barrel  of  cement  is  47,489  X 
T^w=28.5  Ib. 

"  The  principal  cause  of  lack  of  economy  in  the  rotary 
kiln  is  the  excessive  flue  loss.  Dr.  Joseph  W.  Richard 


POWDERED  COAL  IN  THE   CEMENT  INDUSTRY       75 

has  reported  the  following  distribution  of  heat  losses  in  a 
6by60-ft.  kiln: 

36  per  cent  due  to  excess  air  in  chimney  gases, 
36.1  per  cent  due  to  excess  temperature  of  necessary  products  of 
combustion, 

10.7  per  cent  in  hot  clinker, 

12.8  per  cent  in  radiation  and  convection. 

"  The  above  investigation  indicates  about  72  per  cent 
of  flue  loss  of  which  one-half  is  due  to  poor  operation  and  is 
preventable. 

"  In  order  to  utilize  the  waste  heat  in  the  stack,  it  was 
arranged  in  the  Cayuga  Lake  plant  to  pass  the  discharge 
gases  of  two  kilns  through  a  boiler  and  an  economizer,  the 
draft  being  maintained  by  a  fan.  It  was  also  arranged  to 
heat  the  air  entering  the  kilns  by  drawing  it  through  the  hot 
clinker  discharged  from  the  kilns.  The  kilns  were  60  ft.  in 
length,  7.5  ft.  in  diameter  at  the  lower  end  and  6.5  ft.  in  diam- 
eter at  the  upper  end.  The  results  are  shown  in  Table  1. 

TABLE  1 
TWO  KILNS  7J  AND  6§  BY  60  FEET 

Coal  consumed  per  hour,  Ib 1,888 

Clinker  specific  heat,  0.2 

Clinker  produced  per  hour  (CaO  =62  per  cent),  Ib 8,018 

Weight  CaC03  per  hour,  computed,  Ib 8,875 

Moisture  in  raw  material,  3.1  per  cent 

Weight  C02  per  hour  from  material,  Ib 3,660 

Weight  of  air  supplied  per  Ib.  of  coal,  44  per  cent  excess,  Ib .  .  16. 1 

Total  weight  of  air  supplied  per  hour,  Ib 32,297 

Weight  of  air  supplied  by  coal  feeders  per  hour,  Ib 5,850 

Total  weight  of  gases  discharged  per  hour,  Ib 37,749 

Heat  discharged  per  Ib.  of  gas,  0.23X  (1800  - 100),  B.t.u 391 

Area  of  outside  of  kiln,  sq.ft 1,213 

Area  of  hood  exposed,  sq.ft 76 

Gas  leaving  kilns,  deg.  F 1,820 

Air  entering  kilns,  deg.  F 480 

Gas  leaving  boiler,  deg.  F 660 

Gas  leaving  economizer,  deg.  F 450 

Temp,  of  kiln  by  optical  pyrometer,  lower  third,  deg.  F 2350-2960 

Temp,  of  kiln  by  optical  pyrometer,  upper  part,  deg.  F 2960-1800 


76  POWDERED  COAL  AS  A   FUEL 

"  From  the  data  in  Table  1,  Table  2  has  been  computed, 
showing  the  approximate  distribution  of  heat  throughout 
the  process. 

TABLE  2 
APPROXIMATE  DISTRIBUTION  OF  HEAT 

B.t.u.  Per  Cent. 

Heat  entering  kilns  from  clinker  cooler.  .  .  .  2,041,000 
Heat  entering  kilns  from  combustion  of  coal  26,450,000 
Heat  produced  from  chemical  reactions. .  .  .  632,206 
Total  heat  supplied 29,123,206  100.0 


Discharged  from  kiln  to  boiler 14,859,859  51 .2 

Discharged  with  clinker  (8018X2X500) .  .  .     4,409,540  15.1 

CaC03  decomposed  (8875  Ib.  at  765  B.t.u.) .    6,789,375  23 . 3 

126  Ib.  sulphuric  anhydride  liberated 238,140  0 . 8 

252  Ib.  water  evaporated 303,200  1.0 

Radiation  and  unaccounted  for 2,523,092  8.6 


Radiation  per  sq.ft.  of  surface  of  kiln  per  hr..  974 

Heat  absorbed  by  boiler  from  kiln  gases .  .  .  8,798,328  30 . 5 

Heat  absorbed  by  economizer  from  kiln  gases  1 ,1 78,998  4 . 0 

Stack  loss  and  boiler  radiation 4,882,533  16.7        51 . 2 


"  The  investigation  thus  showed  that  about  50  per  cent 
of  the  heat  was  discharged  into  the  stack  and  of  that  amount 
about  68  per  cent  could  be  utilized  in  a  boiler  and  economizer 
so  that  the  ultimate  necessary  flue  loss  was  only  about 
17  per  cent  of  the  heat  in  the  fuel." 

UTILIZATION   OF   WASTE   HEAT 

In  the  cement  industry,  very  few  attempts  have  been 
made  to  utilize  the  heat  of  the  escaping  gases.  The  reason 
why  the  waste  heat  has  not  been  utilized  to  a  greater  extent 
is,  no  doubt,  the  difficulty  of  arranging  and  maintaining 
the  waste  heat  boilers. 

Although  the  temperature  of  the  kiln  stack  gases  has 
been  considerably  reduced  with  the  advent  of  the  long 
kiln,  these  gases  are  still  discharged  at  temperatures  which 


POWDERED  COAL  IN  THE  CEMENT  INDUSTRY      77 

justify  installations  of  equipment  for  the  utilization  of  the 
heat  in  the  large  volumes  of  hot  gases  which  are  constantly 
discharged  from  the  furnace. 

One  method  of  utilizing  the  heat  in  these  gases  stands 
out  prominently  on  account  of  the  economical  results 
obtained.  This  system  contemplates  passing  the  kiln  gases 
through  a  rotary  dryer  placed  directly  behind  the  kiln. 

Such  a  dryer  should  be  so  proportioned  in  relation  to 
the  kiln  that  no  condition  can  be  produced  which  will 
tend  to  reduce  the  capacity  of  the  kiln.  The  diameter 
of  dryer  should  be  at  least  equal  to  the  bore  of  the  kiln, 
so  that  the  dryer  will  not  have  a  dampening  effect  on  the 
draft.  The  kiln  and  dryer  should  be  served  by  separate 
stacks,  of  the  same  diameter  and  height,  so  that  the  kiln 
may  be  operated  either  independently  or  in  unison  with  the 
dryer.  The  stack  chambers  serving  the  kiln  and  the  dryer 
should  be  liberally  proportioned,  so  that  the  gases  will  not 
be  subjected  to  any  interference  as  they  leave  either  the  kiln 
or  the  dryer.  Between  the  kiln  stack  chamber  and  the 
dryer  there  should  be  a  removable  hood,  to  permit  free 
access  to  the  dryer  without  interfering  with  the  continuity 
of  operation  of  the  kiln.  A  rotary  kiln  discharging  its 
waste  gases  through  a  properly  proportioned  dryer  will 
not  only  furnish  sufficient  heat  for  effectually  drying  the 
raw  material  for  a  number  of  kilns,  but  in  addition  will 
produce  as  much  clinker  per  pound  of  coal  as  will  the  same 
size  of  kiln  not  coupled  to  a  dryer.  A  kiln  8  ft.  in  diameter 
120  ft.  long,  coupled  to  a  dryer  7  ft.  in  diameter  and  50 
ft.  long,  kiln  and  dryer  each  being  served  by  a  7-ft.  stack, 
100  ft.  high,  will  have  the  same  capacity  and  will  show  the 
same  fuel  consumption  as  an  ordinary  kiln  of  the  same 
size  discharging  its  gases  of  combustion  to  the  atmosphere 
through  a  stack  of  the  same  dimensions  as  the  stacks  serv- 
ing the  coupled  units. 


CHAPTER  VI 

APPLICATIONS  OF  POWDERED  COAL  TO  REVERBERATORY 

FURNACES 

THE  losses  and  nuisances  arising  from  flue  dust  in  blast- 
furnace smelting,  no  less  than  the  better  fuel  ratio  and 
tonnage  obtained  with  powdered  coal,  are  leading  to  a  grow- 
ing use  of  that  fuel  for  reverbatory  furnaces.  The  latter 
type  of  furnace  also  furnishes  opportunity  for  the  proper 
handling  of  converter  slag  derived  from  basic  ores.  The 
principal  difficulty  attending  this  application  of  powdered 
coal  have  arisen  from  the  choking-up  of  flues  by  adhering 
layers  of  ash:  and  this  difficulty  is  minimized  by  using 
straight  flues  free  from  abrupt  changes  of  area.  The 
deposit  of  a  silicious  surface  over  the  charge  is  made  impos- 
sible if  the  coal  is  positively  and  regularly  fed  to  the  furnace. 

Two  papers  on  this  subject  presented  to  the  American 
Institute  of  Mining  Engineers  in  February,  1915,  describing 
plants  of  the  Canadian  Copper  Co.,  Washoe  Reduction 
Works  and  Anaconda  Copper  Co.,  are  reproduced  here  by 
special  permission  of  the  writers,  the  late  Dr.  David  H. 
Browne,  Metallurgical  Engineer  of  the  International  Nickel 
Co.,  and  Mr.  Louis  V.  Bender  of  the  Anaconda  Copper 
Mining  Company. 

(Paper  by  Dr.  David  H.  Browne) 

CANADIAN    COPPER    CO. 

"  The  use  of  coal  dust  reverberatory  furnaces  was  for 
the  Canadian  Copper  Co.  a  matter  of  necessity,  and  not  of 
choice.  For  twenty  years  smelting  had  been  done  in  blast 
furnaces  alone,  and  with  the  Herreshoff  furnaces  used  prior  to 
1904  there  was  no  trouble  in  treating  fine  ores.  But  little 

78 


APPLICATIONS  OF  POWDERED   COAL  79 

flue  dust  was  produced,  and  this,  following  the  time-honored 
custom,  was  wet  down  and  put  back  with  the  charge. 
Whether  the  flue  dust  was  really  smelted  or  whether  it  was 
worn  out  by  being  chased  around  in  a  circle,  was  a  problem 
that  troubled  no  one. 

"  With  the  installation  of  modern  blast  furnaces  and  high- 
pressure  blowing  engines  in  1904,  flue  dust  commenced  to 
assert  itself.  Evidently  more  dust  was  made  than  could  be 
smelted,  but  so  many  vital  problems  engaged  attention  at 
this  tune  that  this  minor  question  was  pushed  to  one  side. 

"  In  1906  details  of  blast-furnace  smelting  and  the 
conversion  of  matte  had  been  worked  out  to  a  satisfactory 
conclusion  and  the  ever-increasing  piles  of  flue  dust  and  fine 
ore  in  the  stock  yard  demanded  serious  consideration.  Nu- 
merous experiments  in  sintering,  briquetting,  mixing  with 
converter  slag  to  form  blocks  of  fine  dust  with  green-ore 
fines  and  cement,  and  so  on,  were  undertaken.  None 
of  these  showed  much  promise.  The  problem  was  still 
further  complicated  by  the  question  of  treating  converter 
slag.  The  ore  was  basic,  the  slag  was  not  needed  as  a 
furnace  flux,  and  it  was  felt  that  under  these  conditions  the 
old  method  of  pouring  slag  in  molds  and  remelting  in  the 
blast  furnace  was  an  unnecessary  expense.  If  the  converter 
slag  could  be  settled  in  basic-lined  reverberatory  furnaces,  in 
which  (at  the  same  time)  flue  dust  and  green-ore  fines  could 
be  smelted,  two  problems  might  thus  be  solved  at  once. 

"  Reverberatory  practice  with  these  ores  was,  however, 
unknown.  As  carried  out  in  the  West,  on  silicious  ores 
and  concentrates,  at  least  25  per  cent  of  fuel  was  required, 
and  even  this  ratio  varied  greatly  with  the  skill  of  the 
fireman.  The  lack  of  skilled  labor,  the  difficulty  of  recover- 
ing unburned  coal  from  the  ash  by  water  concentration  dur- 
ing Northern  winters,  and  the  difficulty  of  utilizing  it,  if 
recovered,  in  a  plant  using  no  steam  power;  the  uncer- 
tainty of  the  effect  of  highly  basic  charges  on  the  hearth  and 
walls,  and  entire  local  unfamiliarity  with  reverberatory 
practice,  caused  a  postponement  of  decision. 


80  POWDERED  COAL  AS  A  FUEL 

"  In  the  Engineering  and  Mining  Journal  of  February 
10,  1906,  Mr.  S.  S.  Sorensen,  describing  certain  experiments 
at  the  Highland  Bay  Smelter,  called  the  attention  of  the 
metallurgical  world  to  the  possibilities  of  powdered  coal  as  a 
reverberatory  fuel.  While  Mr.  Sorensen's  experiments 
did  not  lead  to  the  adoption  of  powdered  coal  at  Highland 
Bay,  they  showed  clearly  that  increased  tonnage  could 
be  attained  with  decrease  fuel  consumption,  and  that  such 
difficulties  as  he  encountered  were  largely  mechanical  and 
presumably  removable.  Mr.  Sorensen  was  probably  the 
pioneer  in  the  use  of  powdered  coal  in  reverberatory  furnaces. 

"  His  experiences  were  supplemented  by  Mr.  Charles 
Shelby,  who  hi  an  able  article  in  the  Engineering  and  Mining 
Journal  of  March  14,  1908,  described  his  investigation  of 
the  use  of  powdered  coal  in  a  reverberatory  furnace  at  Cana- 
nea.  Mr.  Shelby  experienced  trouble  from  the  sticking 
of  ash  in  the  flues  and  from  the  formation  of  a  silicious 
blanket  over  his  charge;  but,  until  blocked  by  these  con- 
ditions, he  attained  better  results,  both  in  tonnage  and  in 
fuel  ratio,  than  had  been  obtained  by  grate  firing.  A 
profitable  contract  for  the  purchase  of  fuel  oil  led  to  the 
discontinuance  of  these  experiments,  but  enough  had  been 
done  to  show  that  the  subject  was  worthy  of  further  investi- 
gation. 

"  In  October,  1909,  the  Tepoe  Valley  smelter  (of  which 
Mr.  Sorensen  was  the  Superintendent)  was  visited  by  the 
writer.  We  went  over  the  details  of  the  Highland  Bay 
experiments  together  and  agreed  that  with  proper  attention 
to  structural  and  mechanical  details  the  troubles  there  experi- 
enced would  be  avoided.  In  the  same  month  Mr.  Shelby 
was  interviewed  regarding  the  difficulties  encountered  at 
Cananea.  These  also  seemed  avoidable.  It  was  evident 
that  if  the  problem  could  be  worked  to  a  successful  issue, 
the  fuel  ratio,  then  usually  about  4  to  1,  might  be  raised  to 
6 J  or  7  to  1.  This  warranted  considerable  expenditure  in 
working  out  the  details  of  practice. 

"  In  visiting  all  of  the  prominent  Western  smelters  in 


APPLICATIONS  OF  POWDERED   COAL  81 

that  year  (1909),  it  was  found  that  the  proposal  to  use  pow- 
dered coal  on  a  large  scale  was  received  with  more  interest 
than  enthusiasm.  As  a  rule,  investors  were  skeptical  as  to 
the  expediency  of  starting  a  new  plant  on  a  practically 
unproved  method. 

"  During  the  fall  of  1909  Mr.  George  E.  Silvester  visited 
the  cement  factories  in  the  Eastern  states  in  order  to  study 
the  proper  method  of  grinding  and  burning  coal.  His 
report  confirmed  the  opinion  that  the  process  was  prac- 
ticable, and  during  the  winter  plans  were  drawn  for  a  rever- 
beratory  furnace  plant  to  use  powdered  coal  as  a  fuel. 

"  The  mechanical  difficulties  encountered  at  Highland 
Bay  and  at  Cananea  consisted  chiefly  of  two  things,  viz. : 
the  stoppage  of  flues  with  accumulations  of  ash,  and  inter- 
ruptions and  irregularities  in  the  coal-dust  feed.  It  had  been 
demonstrated  in  cement  plants,  however,  that  the  operations 
of  feeding  and  burning  powdered  coal  could  be  made  quite 
as  continuous,  as  uniform,  and  as  easily  regulated  as  feeding 
fuel  oil;  provided  only,  that  proper  methods  were  used  hi 
the  preparation  of  the  coal. 

"  A  plant  equipped  with  the  latest  appliances  for  dry- 
ing and  pulverizing  coal  was  therefore  designed,  to  be  located 
in  a  fireproof  building,  entirely  separated  from  the  rever- 
beratory  furnace  building.  Especial  care  was  taken  to 
specify  that  all  bins,  conveyors,  etc.,  for  the  powdered  coal, 
be  made  as  nearly  dust-proof  as  possible  by  the  use  of 
rubber  gaskets,  to  eliminate  the  danger  of  dust  explosions. 
To  circumvent,  if  possible,  the  trouble  from  accumulations 
of  coal  ash,  an  entirely  new  arrangement  of  furnace  flue 
was  designed,  the  idea  being  to  eliminate  the  several  right- 
angled  bends  in  common  use,  and  to  provide,  as  far  as 
possible,  a  straightway  course  for  the  gases.  In  following 
out  this  idea,  the  skimming  door  was  taken  from  its  tradi- 
tional position  at  the  end  of  the  furnace  and  placed  on 
the  side,  entailing  the  sacrifice,  apparently,  of  nothing  but 
the  tradition. 

"  As  the  furnishing  of  steam  power  from  waste  gases  was 


82  POWDERED  COAL  AS  A  FUEL 

not  an  essential  feature  of  the  installation,  hydro-electric 
power  being  used  in  the  plant,  the  waste  heat  boiler  was  made 
entirely  a  secondary  consideration,  and  was  situated  so  as 
not  to  interfere  in  any  way  with  the  straightway  idea, 
whether  in  use  or  by-passed. 

"  In  February,  1910,  in  company  with  Mr.  Silvester, 
the  Western  smelters  were  visited  to  obtain  information  on 
reverberatory  practice.  Mr.  Sorensen  was  keenly  inter- 
ested in  Mr.  Silvester's  plans,  in  which  he  advised  a  few 
modifications  of  minor  details,  while  approving  the  ideas  as 
a  whole. 

"  In  April,  1910,  the  Canadian  Copper  Co.  authorized 
construction,  and  work  was  begun  at  once.  As  the  entire 
site  of  the  proposed  plant  had  to  be  raised  11  ft.  above  the 
yard  level,  and  a  large  amount  of  rock  cutting  and  filling 
was  necessary  on  the  hillside  where  the  bins  and  approaches 
were  planned,  active  construction  did  not  commence  until 
December  23,  1911. 

"  As  built,  the  original  furnaces  were  lined  with  basic 
brick,  and  the  hearth  was  an  inverted  arch  of  magnesite. 
The  furnaces  went  into  operation  before  any  means  of  dry- 
ing the  flue  dust  was  provided,  and  during  the  winters  of 
1911  and  1912,  a  large  amount  of  charge,  wet  and  frozen  as  it 
came  from  the  piles,  was  shoveled  in  through  the  doors  of 
the  furnace.  All  the  converter  slag  was  poured  in;  at  first 
through  a  door  near  the  fire  end,  just  as  scrap  is  charged  in 
an  open-hearth  furnace. 

"  The  introduction  of  so  much  cold  air  and  cold  material 
made  it  impossible  to  attain  any  satisfactory  fuel  ratio.  Dur- 
ing the  first  five  months,  21,406  tons  of  cold  charge  and 
43,463  tons  of  converter  slag  were  smelted  with  9609  tons 
of  coal.  This  shows  a  ratio  of  6.7  tons  of  total  charge  per 
ton  of  coal,  but  of  only  2.2  tons  of  cold  charge  per  ton  of  coal. 
However,  as  the  cold  charge  was  wet  and  often  frozen, 
better  results  could  probably  not  be  expected. 

"  The  combustion  of  fuel  was  satisfactory  from  the  start, 
no  trouble  being  experienced  either  in  grinding  or  in  burning 


APPLICATIONS  OF  POWDERED  COAL  83 

the  coal.  The  ash,  while  working  on  cold  charges,  choked 
and  clogged  the  flue  at  the  throat.  This  difficulty  was  not 
eliminated  until  later,  when  hot  calcines  were  used  and  a 
larger  tonnage  was  smelted.  In  general,  the  more  slowly 
the  furnace  worked,  the  colder  was  the  ash  and  the  more  it 
stuck  and  accumulated;  while  the  faster  it  was  driven  the 
less  did  the  ash  hang  back  in  the  furnace.  Under  present 
conditions,  with  rapid  smelting,  the  ash  is  a  negligible 
factor. 

"  In  the  summer  of  1912  the  roof  and  side  walls  were 
repaired,  and  some  facilities  provided  for  drying  the  charge. 
In  the  winter  of  1912  four  wedge  furnaces  were  built  to 
roast  green-ore  fines.  These  went  into  operation  in  March, 
1913.  At  this  date  we  ceased  to  run  converter  slag  in  the 
reverberatory  furnaces,  since  with  the  opening  of  No.  3 
mine  the  blast  furnace  charge  became  more  silicious  and 
slag  could  be  used  economically  as  a  flux. 

"  During  the  next  year  very  pronounced  improvements 
were  made  by  Mr.  Agnew,  then  Superintendent  of  the  smel- 
ter, who  with  his  foremen,  Messrs.  Kent,  McAskill  and 
Mason,  worked  out  and  adapted  to  our  use  a  modification 
of  the  Cananea  system  of  side-fettling.  Long  and  shallow 
pockets  were  provided  along  the  side  wall,  through  holes 
in  which  the  green-ore  fines  were  fed  to  protect  the  sides. 
This  naturally  led  to  bricking  up  all  the  doors  on  the  fur- 
nace, and  marked  improvement  resulted  from  the  exclusion 
of  cold  air  and  the  insulation  of  the  walls  by  a  non-conduct- 
ing and  continuously  renewed  blanket  of  fines. 

"  As  the  walls  were  thoroughly  protected  by  the  charge 
thus  introduced,  the  use  of  basic  brick  in  the  walls  and  hearth 
was  no  longer  necessary,  and  the  next  change,  in  October, 
1913,  was  to  the  silicious  bottom  and  brick  walls  customary 
in  Western  smelters. 

"  In  1914  the  fuel  ratio  and  furnace  practice  were 
steadily  improving.  The  figures  for  the  first  three  months 
in  1914,  one  reverberatory  being  in  use,  are  given  in  the 
tabulation  below. 


84 


POWDERED  COAL  AS  A  FUEL 
1914— CANADIAN  COPPER  COMPANY 


January. 

February. 

March. 

Furnace  days  

31 

28 

31 

Calcines  tons  

10,020 

9460 

10860 

Blast  furnace  flue  dust,  tons.   .  . 

906 

922 

847 

Wedge  furnace,  flue  dust,  tons  .  .  . 
Converter  slag  tons 

171 
69 

193 
248 

180 

o 

Green-ore  fines  and  samples,  tons. 

1,731 

1,326 

2,308 

Total  charge  tons 

12897 

12  149 

14  195 

Coal  tons 

2575 

2  150 

2094 

Charge  per  day,  tons  

416 

434 

458 

Coal  per  day,  tons  

83 

77 

67 

Ratio  of  charge  to  fuel  

5.0 

5.65 

6.77 

"  In  the  summer  of  1914  a  change  was  made  in  grinding 
the  ore  fines  for  the  wedge  furnace.  The  ore,  which  was 
previously  too  coarse  to  make  a  good  calcination,  was  treated 
in  ball  mills,  and  screened,  so  that  only  about  14  per  cent 
remained  on  a  20-mesh  screen,  instead  of  the  former  40 
per  cent.  This  finer-crushed  ore  could  not  be  produced  in 
sufficient  quantity  to  keep  the  furnace  up  to  its  capacity. 
Furthermore,  when  the  calcines  dropped,  on  account  of 
this  finer  grinding  of  the  ore,  from  13  per  cent  of  sulphur  to 
7  or  8  per  cent,  the  production  of  slag  increased  and  the 
production  of  matte  fell  off.  These  conditions,  with  the 
shortage  of  calcines,  militated  against  a  high  ratio  of  charge 
to  fuel,  and  in  June,  1914,  the  fuel  ratio  was  5.35. 

"  The  above  narrative  is  introduced  to  show  the  gradual 
development  of  the  process,  and  the  conditions  which  have 
brought  about  changes  from  the  original  plans.  We  now 
consider  some  details  of  construction. 

"  The  area  occupied  by  the  reverberatory-furnace  build- 
ing was  raised  about  11  ft.  above  the  surrounding  yard  by 
pouring  furnace  slag  between  concrete  retaining  walls, 
which  were  protected  as  the  filling  progressed  by  spreading 


APPLICATIONS   OF  POWDERED   COAL  85 

clay  against  the  concrete.  At  distances  of  56  ft.  apart, 
on  the  center  lines  between  the  furnaces,  tunnels  12  ft. 
wide  were  provided  in  this  slag  foundation.  These  tunnels 
were  to  carry  tracks  so  that  the  reverberatory  furnaces 
built  on  this  poured-slag  area  could  be  tapped  into  pots 
at  the  level  of  the  yard.  The  furnaces  are  skimmed  into 
25-ton  pots  at  the  yard  level.  (Figs.  27  and  28.) 

"  Under  the  lines  where  the  furnace  side  walls  were  to 
go,  concrete  footings  were  introduced,  and  between  these 
footings  transverse  rods  were  laid  in  iron  pipes.  Then  the 
slag  pouring  was  continued.  The  tie  rods  carried  anchor- 
plates  which  held  the  footings  under  the  furnace  walls  to- 
gether and  took  up  the  lateral  thrust  at  the  foot  of  the  side 
buckstays.  Under  the  furnace  hearth,  the  slag  filling  rose 
12  in.  above  these  concrete  footings.  On  the  concrete 
footings  were  erected  the  silica-brick  furnace  walls. 

"  The  horizontal  dimensions  of  the  furnace  are  23  ft. 
6  in.  by  116  ft.  9  in.,  outside  of  the  brickwork. 

"  The  side  walls  arising  from  the  footings  inclose.  12  in. 
of  poured  slag  which  extends  under  the  silica  hearth.  The 
side  walls  are  carried  up  27  in.  in  thickness  to  a  height  of 
3  ft.  4f  in.,  making  the  total  height  of  the  side  walls  8  ft., 
9J  in.,  up  to  the  point  where  the  cast-iron  skew  block  is 
laid  for  the  arch  roof.  This  height  is  maintained  for  a 
distance  of  34  ft.  from  the  fire  end,  from  which  point  the 
skewbacks  slope  down  to  correspond  with  the  slope  of  the 
arch  roof  referred  to  above. 

"  The  end  or  fire  wall  is  3  ft.  6  in.  wide  at  the  bottom 
for  a  height  of  2  ft.  and  is  then  stepped  back  to  22|  in.  at  a 
height  of  3  ft.  8  in.,  and  again  stepped  back  to  a  width  of 
13^  in.  at  a  height  of  6  ft.  3  in.  At  the  other  end  of  the 
furnace,  commonly  called  the  skimming  end,  or  front,  the 
construction  is  very  heavy,  to  resist  the  end  thrust  of  the 
hearth.  It  consists  of  a  brick  block,  6  ft.  wide  and  3  ft.  high, 
which  is  stepped  back  to  a  width  of  2  ft.  6  in.  at  the  throat, 
at  which  point  it  is  4  ft.  9  in.  high. 

"  The  roof  at  the  fire  end  is  of  20-in.  silica  brick.     The 


86 


POWDERED   COAL  AS  A  FUEL 


APPLICATIONS  OF  POWDERED  COAL 


87 


88  POWDERED  COAL  AS  A  FUEL 

height  at  the  skewback  is  7  ft.  9|  in.  above  the  bottom  of  the 
quartz  hearth.  The  central  line  is  9  ft.  9|  in.  above  the  same 
point.  The  radius  is  29  ft.  3|  in.  on  the  under  side  of  the 
arch. 

"  When  the  hearth  is  in,  the  inside  arch  at  the  center 
is  from  7  ft.  9f  in.  to  7  ft.  llf  in.  above  the  top  of  the  hearth 
and  about  6  ft.  8  in.  above  the  skim  line,  or  4  ft.  8  in.  above 
the  center  line  of  the  coal  dust  nozzles. 

"  This  height  of  arch  is  maintained  for  a  length  of  34 
ft.  from  the  outside  or  fire  wall.  In  the  next  12  ft.  the  arch 
drops  22f  in.,  giving  a  height  of  from  5  ft.  11  in.  to  6  ft.  1  in. 
above  the  top  of  the  hearth  and  about  4  ft.  10  in.  above  the 
skim  line.  This  height  is  continued  straight  through  to 
the  throat  of  the  furnace. 

"  The  20-in.  silica  arch  bricks  are  used  for  34  ft.  on  the 
straight  arch  and  for  12  ft.  more  on  the  sloping  arch.  The 
remaining  portion  of  the  roof  is  of  15-in.  brick.  As  the  height 
of  this  roof  has  been  changed  at  various  times,  the  heights 
given  for  the  roof  at  various  points  are  not  exactly  correct 
at  present. 

"  There  are  no  side  doors  to  the  furnace.  As  originally 
built,  doors  were  set  on  12-ft.  centers,  but  these  have  been 
filled  up,  so  that  the  side  walls  present  a  continuous  face 
of  silica  brick  22|  in.  thick. 

"  The  hearth  is  silica  sand  tamped  in  place.  No  binder 
has  been  used,  though  better  results  might  have  been 
obtained  had  some  base  been  introduced.  After  about 
five  days  firing,  50  tons  of  high-grade  matte  were  put  in  to 
saturate  the  bottom.  If  steam  from  the  silica  sand  came 
through  the  walls  the  heat  was  cut  off  for  twenty-four 
hours  to  allow  the  moisture  to  escape.  Some  patches  of 
bottom  floated  up,  but  not  enough  to  interfere  with  sub- 
sequent operations.  This  bottom  is  almost  flat,  being 
24  in.  thick  at  the  end  walls  and  22  in.  thick  at  the  tap 
hole,  36  ft.  from  the  fire  wall.  In  building  the  side  walls, 
wood  strips  were  introduced  to  provide  for  expansion. 
These  wood  strips  (}  in.  thick)  were  placed  every  four  bricks 


APPLICATIONS  OF  POWDERED  COAL  89 

on  the  inside  and  between  every  six  bricks  on  the  out- 
side. As  these  burned  out  they  allowed  the  brick  to  expand 
horizontally.  The  arch  is  laid  in  separate  sections  10  to 
12  ft.  wide,  with  the  usual  wooden  expansion  wedges  2 
or  3  in.  thick  between  sections. 

"  The  side  walls,  built  as  described,  are  carried  straight 
to  a  point  26  ft.  from  the  throat,  where  they  curve  inwardly, 
the  space  of  19  ft.  9  in.  between  them  being  narrower  up 
along  the  line  of  gradually  increasing  curvature  to  a  width 
of  8  ft.  8  in.  at  the  throat.  At  this  point  the  opening  is  4  ft. 
3  in.  high  at  the  center  and  3  ft.  9  in.  at  the  sides.  The  arch 
here  is  about  4  ft.  8  in.  above  the  skimming  line. 

"  From  the  throat  a  straight  flue  8  ft.  8  in.  wide  leads  to 
the  waste  heat  boilers  and  to  the  stack.  Openings  are 
provided  along  the  side  of  this  flue  for  cleaning  out  any 
deposited  ash.  An  opening  opposite  the  throat  is  provided 
by  raising  the  bottom  of  this  flue  about  18  in.  above  the 
throat  and  introducing  a  door  in  the  space  thus  formed. 
This  is  useful  for  removing  any  accretions  of  ash  fused  in  the 
throat.  The  skimming  door  is  placed  on  one  side  of  the  fur- 
nace, 16  ft.  6  in.  back  from  the  throat.  This  door,  2  ft.  6  in. 
wide  by  15  in.  high,  allows  slag  to  run  off  down  to  a  skimming 
line  14|  in.  above  the  hearth  at  the  tap  hole.  The  slag 
can  rise  6  in.  above  this  line  before  reaching  the  level  of 
the  side  doors  now  bricked  up.  Outside  the  skimming 
door  a  cast-iron  clay-lined  box  is  provided  to  trap  any  matte 
carried  over.  From  this  the  cast-iron  slag  launder  curves  to 
a  line  almost  parallel  with  the  furnace  and  delivers  the  slag 
into  25-ton  pots,  which  are  brought  in  on  track  at  right 
angles  to  the  furnace  under  the  flue. 

"  The  furnace  is  fed  in  a  rather  peculiar  way.  When 
the  furnace  was  started,  almost  all  of  the  charge  was  intro- 
duced through  two  charge  hoppers  near  the  fire  end,  as  in 
usual  Western  practice.  The  first  hopper  delivered  through 
two  openings,  11  in.  hi  diameter  and  7  ft.  6  in.  apart,  and  8 
ft.  from  the  outside  of  the  fire  wall.  The  second  hopper  de- 
livered through  two  similar  openings  18  ft.  from  the  fire  wall. 


90  POWDERED  COAL  AS  A  FUEL 

"  At  present  almost  all  of  the  charge  is  introduced  through 
hoppers  along  the  side  walls.  Directly  over  the  side  walls, 
at  the  fire  end  of  the  furnace,  large  bins  are  provided,  which 
discharge  into  small  bottom-dump  cars.  These  cars  run 
on  24-in.  tracks  which  are  supported  from  overhead.  Under 
these  tracks  a  long  trough  runs  down  each  side  of  the  fur- 
nace just  above  the  side  walls.  These  troughs  are  filled 
from  the  cars  on  the  track  above  them.  Each  trough  has 
openings  in  the  bottom,  2  ft.  apart,  which  openings  com- 
municate by  a  slide  gate  with  6-in.  iron  pipes.  These  pipes 
pass  into  holes  drilled  in  the  roof  bricks,  which  allow  the 
charge  introduced  through  these  openings  to  slide  down 
on  the  side  walls  over  which  this  charge  forms  an  almost 
continuous  blanket.  As  there  are  no  doors  on  the  furnace, 
and  as  the  6-in.  pipes  are  clayed  into  the  openings  in  the 
roof,  it  follows  that  no  air  is  introduced  into  the  furnace 
except  what  is  purposely  introduced  at  the  fire  end. 

"  These  pipes  form  a  continuous  line  of  charging  holes, 
which  extend  the  entire  length  of  the  furnace.  The  charge 
on  the  side  opposite  the  slag  door  is  fed  all  the  way  to  the 
throat.  On  the  slag  side  it  is  fed  along  as  far  as  the  slag 
door  and  no  farther,  as  the  cold  air  coming  in  while  skimming 
cools  the  walls  from  the  skim  door  to  the  throat  and  obviates 
the  necessity  of  charging  beyond  this  point.  Six  similar 
openings  are  used  in  the  fire  wall. 

"  The  walls  are  held  in  place  by  12-in.  I-beams  in  pairs, 
with  a  space  of  5  ft.  between  each  pair,  which  form  the  side 
braces.  These  are  wedged  in  at  the  bottom,  by  wooden 
wedges,  against  an  iron  strap  in  the  concrete  footings. 
The  concrete  footings  are  tied  together  as  previously  de- 
scribed by  l|-in.  rods  passing  across  the  furnace. 

"  The  coal  dust  is  introduced  through  five  pipes,  5  in. 
in  diameter.  One  of  these  pipes  is  on  the  center  line  of  the 
furnace,  the  others  are  in  horizontal  line  with  it  at  a  distance 
of  3  ft.  3  in.  from  center  to  center.  These  pipes  are  5  ft. 
2  in.  above  the  bottom  of  the  sand  hearth,  or  3  ft.  2  in. 
above  the  top  of  this  hearth.  They  are  about  2  ft.  above 


APPLICATIONS  OF  POWDERED   COAL  91 

the  skimming  line  of  the  charge  and  the  central  pipe  is  about 
4  ft.  8  in.  below  the  highest  point  of  the  roof. 

POWDERED    COAL   APPARATUS 

"  The  coal  as  received  is  f  in.  and  under  in  size  and  con- 
tains about  7  per  cent  of  moisture.  It  is  dried  in  a  Ruggles- 
Coles  dryer,  70  in.  in  diameter  and  35  ft.  long.  One  ton  of 
coal  burned  on  the  grate  dries  40  to  50  tons  of  slack  coal 
to  about  0.5  per  cent  of  moisture,  which  increases  to  2.4 
per  cent  of  moisture  after  grinding.  About  10  tons  of  slack 
are  dried  per  hour  of  running  time.  The  coal  is  ground  in 
Raymond  impact  mills.  About  95  per  cent  passes  a  100- 
mesh  and  80  per  cent  a  200-mesh  screen. 

"  The  powdered  coal  is  sucked  by  a  fan  to  separators 
above  the  roof  of  the  dryer  building  and  slides  downward  into 
a  screw  conveyer  which  delivers  it  into  bins  at  the  fire  end 
of  the  reverberatory  furnace.  The  dust  is  fed  from  these 
bins  by  Sturtevant  automatic-feed  screw  conveyers,  one  for 
each  nozzle,  the  speed  of  which  can  be  regulated.  These 
screws  carry  the  dust  forward  and  drop  it  into  the  air 
nozzles  about  2  ft.  from  the  point  where  the  nozzles  enter 
the  furnace.  Any  coal  delivery  pipe  can  be  closed  off  by  a 
slide  gate,  and  any  screw  conveyer  can  be  stopped  by  dis- 
connecting the  bevel  gears  attached  thereto.  In  this  way 
any  desired  number  of  the  five  burners  can  be  run,  and  at  any 
desired  speed  within  wide  limits.  The  amount  of  air 
delivered  to  each  nozzle  can  be  varied  at  will  or  cut  off 
entirely. 

"  As  a  rule  the  five  burners  are  in  operation.  Each 
delivers  about  13.5  tons  of  coal  dust  a  day  or  about  19  Ib. 
of  coal  per  minute  at  the  furnace.  The  total  coal  blown  in 
is  about  67  tons  per  day. 

'  The  dust  drops  from  the  conveyers  into  the  air  pipes, 
which  carry  it  forward  into  the  furnace.  The  air  is  supplied 
by  a  4-ft.  Sturtevant  fan,  running  at  1300  to  1400  revolutions 
per  minute.  The  air  supplied  by  this  fan  is  insufficient  for 
the  combustion  of  the  coal.  Openings  are  left  in  the  end 


92  POWDERED   COAL  AS  A  FUEL 

wall  between  the  coal  burners.  These  openings  are  stopped 
by  loose  bricks,  so  that  the  amount  of  air  is  readily  controlled. 
The  draft  at  the  fire  wall  is  about  0.25  in.  of  water  and  at  the 
throat  the  maximum  draft  is  about  1.2  in.  The  combus- 
tion is  very  good.  One  test  made  for  ten  days  (Jan.  9 
to  19,  1914)  showed  the  following  averages: 

Coal  consumption,  tons  in  24  hours 69.7 

Gas  temperature  at  throat,  deg.  C 922 

S02  and  C02,  per  cent 12.3 

Oxygen,  per  cent 6.5 

S03,  per  cent 1 . 14 

"  During  this  test  the  average  charge  was  409  tons  in 
24  hours.  This  shows  a  ratio  of  5.9  parts  of  charge  to  1 
part  of  coal,  but  much  higher  ratios  have  been  attained. 
The  average  for  March,  1914,  was  6.84.  This  coal  ratio 
depends  largely  upon  the  composition  of  the  charge  and  the 
nature  of  the  slag  produced. 

"  A  criticism  might  be  made  of  the  low  temperature  of 
the  gases  at  the  throat,  922°  C.  The  usual  practice  in 
Western  smelters  is  to  carry  a  temperature  of  1200  to  1300° 
C.  at  this  point,  and  it  might  be  thought  that  this  low  tem- 
perature indicates  inefficient  firing.  The  fact  is  that  the 
heat  of  combustion  is  utilized  in  smelting  ore  along  the  side 
walls,  and  consequently  the  escaping  gases,  having  done 
more  work  than  is  usually  the  case,  are  relatively  cold.  The 
function  of  a  reverberatory  furnace  is  to  smelt  ore,  and  not 
to  raise  steam,  and  for  this  reason  the  more  heat  that  is 
absorbed  from  the  coal  gases  in  the  furnace,  the  more 
efficient  is  the  operation  and  the  cooler  are  the  escaping 
gases. 

"  The  great  advantage  of  coal-dust  firing  in  applications 
of  this  sort  is  the  absence  of  the  usual  breaks  in  the  tem- 
perature curve  due  to  grating  or  cleaning  the  hearth,  and  as 
a  consequence  a  greatly  increased  tonnage  and  fuel  ratio. 
The  '  operation  of  firing,  being  purely  mechanical,  comes 
under  the  immediate  and  direct  control  of  the  furnace 


APPLICATIONS  OF  POWDERED  COAL  93 

foreman  and  responds  instantly  to  his  regulation.  In 
addition  to  this,  the  peculiar  method  of  feeding  by  almost 
continuous  charging  obviates  breaks  in  the  temperature 
curve  due  to  charging  or  ordinary  fettling.  For  these  two 
reasons  the  chart  of  temperature  shows  a  horizontal  line, 
rising  or  falling  in  almost  exact  accordance  with  the  speed  of 
the  coal-feeding  device. 

"  The  maximum  bath  of  matte  and  slag  is  22  in.  deep. 
A  constant  bath  of  8  in.  of  matte  is  carried.  This  matte 
lies  6  in.  below  the  skimming  plate,  so  that  after  skimming 
there  are  6  in.  of  slag  and  8  in.  of  matte  left  in  the  furnace, 
making  a  total  minimum  depth  of  14  in.  The  skimming 
door  is  banked  up  8  in.  with  sand,  so  that  just  before  skim- 
ming the  slag  is  14  in.  deep.  As  the  charge  along  the  side 
walls  occupies  a  great  deal  of  room  there  is  never  at  any  time 
more  than  40  or  50  tons  of  slag  in  the  furnace. 

"  In  rebuilding  this  reverberatory  or  in  designing  a  new 
plant,  the  hearth  should  be  widened  to  provide  for  a  larger 
body  of  matte,  which  experience  has  shown  to  be  necessary. 
As  this  method  of  burning  coal  and  of  admitting  the  charge 
into  the  furnace  bids  fair  to  come  into  general  use,  it  is 
expected  that  many  changes,  both  in  construction  and 
operation,  will  be  introduced.  There  is  no  doubt  that 
reverberatory  smelting  along  these  lines  will  become  cheaper 
than  blast-furnace  smelting  and  that  a  wider  range  of  ores 
can  be  used  in  such  a  furnace  than  in  the  old  style  coal  or 
oil  furnace." 

(Paper  by  Mr.  Louis  V.  Bender.) 

WASHOE    REDUCTION   WORKS 

"  After  investigating  the  work  of  coal  dust  at  the  Cana- 
dian Copper  Co.  the  management  of  the  Washoe  plant 
decided  to  experiment  with  and  ascertain  the  advantages 
of  using  powdered  coal  as  fuel  in  their  reverberatories. 
Consequently,  during  the  month  of  June,  1914,  one  of  their 
reverberatory  furnaces  was  changed  to  use  powdered  coal  as 


94  POWDERED   COAL  AS  A  FUEL 

fuel.  The  results  obtained  by  this  method  of  firing  are 
gratifying  and  show  a  decided  saving  in  cost  of  smelting 
as  compared  with  grate  firing  of  ordinary  coal. 

"  The  furnace  as  remodeled  is  124  ft.  long  by  21  ft.  wide, 
and  varies  in  height  from  8  ft.  6  in.  at  the  back  to  5  ft.  7  in. 
at  the  skimming  end.  The  general  construction  of  the  fur- 
nace is  similar  to  that  of  other  furnaces  at  this  plant. 
There  are  no  side  doors  to  this  furnace,  as  it  was  thought  that 
with  the  present  arrangement  for  feeding  no  fettling  or 
claying  would  be  required.  The  interior  of  the  furnace  can 
be  inspected  through  the  burner  portholes,  after  shutting 
off  the  burners  and  giving  a  few  seconds'  time  for  the  gases 
inside  the  furnace  to  clear  away.  The  charging  is  done  on 
either  side  of  the  furnace  from  longitudinal  hoppers,  ex- 
tending a  distance  of  74  ft.  from  the  back  end  of  the  furnace. 
Leading  from  the  hoppers  into  the  furnace  are  6-in.  pipes 
spaced  19J  in.  apart,  through  which  the  charge  is  intermit- 
tently dropped.  The  charge  is  kept  well  above  the  slag 
line  at  all  times ;  in  this  way  the  side  walls  are  protected  and 
no  fettling  is  needed  on  this  portion  of  the  furnace.  The 
remainder  of  the  furnace  requires  fettling.  After  operating 
for  three  months,  it  was  found  that  the  bricks  were  eaten 
into  along  each  side  wall  from  the  skimming  door  back  to 
the  point  where  the  charge  had  been  dropped.  The  depth 
of  this  cutting  away  was  8  in.  close  to  the  front  end  and 
gradually  tapered  to  zero  at  a  distance  of  50  ft.,  and  was 
greater  on  the  side  of  the  furnace  having  the  larger  flue 
connection.  Hoppers  will  be  put  in  for  the  entire  length  of 
furnace,  from  which  fettling  material  will  be  dropped,  to 
prevent  this  cutting. 

"  After  a  run  of  three  months  the  roof  was  in  excellent 
condition.  At  the  back  of  the  furnace  the  bricks  were  not 
cut  into  at  all;  at  30  ft.  from  the  back  end  they  were  eaten 
away  2  in.,  but  at  60  ft.  distant  they  were  as  put  in.  The 
roof  is  20  in.  thick.  After  operating  for  a  while  trouble  was 
encountered  in  tapping  the  matte.  The  tap  hole  was  on  the 
east  side  of  the  furnace  83|  ft.  from  the  front  end.  Charging 


APPLICATIONS   OF  POWDERED  COAL 


95 


could  not  be  done  over  the  tap  hole,  or  for  a  distance  of 
several  feet  on  either  side;  also,  owing  to  the  method  of 
charging,  matte  accumulated  in  the  front  of  the  furnace 
and  could  not  be  completely  drained  through  the  side  tap 
hole. 

"  When  the  furnace  was  down  for  fettling  in  front,  it 
was  seen  that  the  calcines  fed  into  the  furnace  sloped  very 
gently  from  either  side  to  the  center.  This,  of  course,  took 
up  the  space  which  in  other  furnaces  is  filled  with  matte 
and  forced  the  matte  to  the  front  of  the  furnace  and  also 
prevented  its  being  drawn  out  at  the  side  tap  hole.  The 
furnace  will  not  hold  more  than  50  tons  of  matte.  The 
other  furnaces  hold  175  tons.  It  was  finally  decided  to  tap 
the  furnace  at  the  front.  A  suitable  runway  was  put 
in  and  a  tap  hole  made  at  the  side  of  and  below  the  skim- 
ming door,  and  all  of  the  matte  was  tapped  therefrom. 
About  35  tons  of  matte  are  tapped  per  shift.  The  furnace 
is  skimmed  three  times  per  shift.  The  gases  are  taken  from 
the  furnace  through  brick  flues  to  either  of  the  two  batteries 
of  Stirling  boilers,  each  battery  developing  650  horse-power. 
One  of  the  flue  connections  was  left  as  before,  with  a  cross- 
sectional  area  of  13J  sq.ft.;  the  other  flue  connection  has  a 
cross-sectional  area  of  40  sq.ft.  The  smaller  flue  con- 
nection is  used  whenever  it  is  necessary  to  clean  the  boilers 
connected  with  the  larger  flue.  This  occurs  once  a  month 
and  lasts  for  a  period  of  three  days,  during  which  time  the 
tonnage  smelted  is  considerably  less  than  when  using  the 
larger  flue.  The  following  figures  verify  this  statement: 


Cross-section  of 
Flue,  Square  Feet. 

Average  of  Tons. 

Fuel  Ratio. 

13| 

3  days  405 

6.8 

40 

3  days  before  cleaning  497 

6.7 

3  days  after  cleaning    539 

7.3 

96  POWDERED  COAL  AS  A  FUEL 


ANACONDA   PLANT 

"  The  following  equipment  is  installed.  It  is  larger  than 
is  required  for  one  furnace,  but  was  installed  with  the  idea 
in  mind  of  finally  equipping  the  entire  reverberatory  plant 
for  coal-dust  firing. 

"  The  coal  from  the  storage  bin  is  fed  into  a  30  by 
30-in.  Jeffrey  single  roll  crusher,  where  it  is  reduced  to  1  in. 
maximum  size.  After  passing  a  magnetic  separator,  it  is 
elevated  and  fed  by  gravity  into  a  40-ft.  by  6  ft.  8  in. 
Ruggles-Coles  dryer.  The  dryer  consists  of  two  cylinders, 
the  one  within  the  other.  Blades  of  angle  iron  are  fastened 
to  the  inner  side  of  the  outer  cylinder  and  the  outer  side  of 
the  inner  cylinder,  so  arranged  that  as  the  dryer  revolves 
the  material  fed  into  the  space  between  the  cylinders  is 
lifted  and  dropped  onto  the  inner  cylinder  and  at  the  same 
time  carried  to  the  discharge  end.  The  outer  cylinder  at 
the  discharge  end  extends  beyond  the  inner  cylinder  and  has 
a  revolving  head  riveted  to  it;  on  the  inside  of  the  head  are 
buckets  which  lift  the  coal  and  deliver  it  out  through  the 
central  casting.  It  takes  a  particle  about  thirty  minutes 
to  pass  from  feed  end  to  discharge  end  of  the  dryer.  At 
the  feed  end  the  inner  cylinder  is  extended  beyond  the  outer 
cylinder  and,  passing  through  a  stationary  head,  is  connected 
with  a  fire  box.  The  gases  are  drawn  from  the  fire  box  by 
means  of  a  72-in.  Sturtevant  fan,  forward  through  the  inner 
cylinder  and  back  through  the  annular  space  between  the 
cylinders  to  the  stack.  This  exhaust  fan  is  placed  on  top  of 
the  fire  box  and  is  connected  to  the  dryer  by  means  of 
a  30-in.  sheet-iron  pipe.  The  fire  box  is  fed  with  lump  coal. 
The  capacity  of  a  dryer  depends  upon  the  moisture  in  the 
coal  and  the  speed  of  the  fan.  With  Diamondville  coal,  18 
tons  are  dried  per  hour.  During  the  month  of  Septem- 
ber, 1914,  30  tons  of  coal  were  used  to  dry  1,984.77  tons 
of  coal. 

"  From  the  dryer  the  coal  is  conveyed  by  a  screw  con- 
veyor, and  is  discharged  into  a  steel  bin  above  the  pulverizer, 


APPLICATIONS  OF  POWDERED  COAL  97 

which  is  in  a  separate  building  from  the  dryer.  It  is  not 
well  to  have  the  pulverizer  in  the  same  building  with  the 
dryer,  for  the  reason  that  if  an  accident  should  occur,  caus- 
ing the  coal  to  overflow,  it  might  then  be  drawn  into  the 
fire  chamber  of  the  dryer  and  cause  a  fire,  with  possible  injury 
to  employees. 

"  The  Raymond  five-roller  mill  is  used.  It  has  an 
average  hourly  capacity  of  4|  tons  (see  Chapter  III).  A  fan 
is  connected  to  this  mill,  from  which  air  is  admitted  under- 
neath the  grinding  surface.  The  material  is  taken  away 
by  the  air  current  as  quickly  as  it  is  reduced  by  the  rolls, 
and  blown  into  a  cyclone  dust  collector  placed  20  ft.  above  the 
pulverizer.  The  mill  is  thus  free  of  fine  material.  The 
collector  is  of  galvanized  steel,  cone  shaped,  and  has  a  return 
air  pipe  leading  from  it  to  the  housing  around  the  base  of 
of  the  mill.  A  surplus  air  pipe  from  this  return-air  pipe 
relieves  the  back  pressure  and  is  an  outlet  for  any  surplus 
air  that  may  enter  with  the  feed.  An  auxiliary  collector 
is  placed  to  receive  the  dust  escaping  through  this  surplus 
air  pipe. 

"  The  finished  product  is  discharged  through  a  spout 
at  the  bottom  of  the  dust  collector,  and  is  taken  by  a  screw 
conveyor  to  a  bin  placed  near  to  and  above  the  furnace. 

"  The  coal  from  the  bin  is  introduced  into  the  furnace  by 
means  of  an  air  current  delivered  through  five  '  burners/ 
The  air  current  is  produced  by  a  No.  11  Buffalo  fan  at  a 
pressure  of  10  oz.  and,  by  means  of  a  pipe  carrying  a  nozzle, 
is  introduced  into  a  6-in.  pipe  leading  into  the  end  of  the 
furnace.  The  coal  dust,  fed  from  the  bin  by  a  screw  con- 
veyor, drops  upon  this  nozzle  (which  acts  as  a  spreader)  and 
is  mixed  with  the  air  and  taken  into  the  furnace.  A  second- 
ary supply  is  obtained  around  the  portholes  through  which 
the  burners  are  projected  into  the  furnace.  These  port- 
holes are  each  12  in.  in  diameter,  which  leaves  an  annular 
space  3  in.  wide  around  each  of  the  6-in.  pipes.  By  means 
of  suitable  dampers  encircling  the  burners,  this  secondary 
air  can  be  regulated.  Another  source  of  secondary  air  is 


98  POWDERED  COAL  AS  A  FUEL 

through  four  openings  between  and  above  the  burner  ports, 
the  size  of  the  openings  being  regulated  by  putting  in  or 
taking  out  brick.  The  amount  of  coal  fed  is  determined  by 
the  speed  of  the  screw,  which  is  controlled  by  a  Reeves 
variable-speed  regulator.  The  grinding,  conveying,  and 
bin  system,  from  the  dryer  to  the  burners,  is  made  as  air- 
tight as  possible,  with  the  result  that  the  entire  plant  is 
extremely  clean  and  free  from  dust/' 


CHAPTER  VII 
POWDERED  COAL  IN  METALLURGICAL  FURNACES 

POWDERED  coal  is  manifesting  distinct  advantages  for  all 
kinds  of  heating  operations.  With  the  constant  demand  for 
increased  output  in  manufacturing  plants,  the  question  of 
industrial  heating,  important  though  it  is,  is  too  often 
lightly  considered  or  entirely  overlooked,  with  the  result  that 
worth-while  savings  in  cost  of  manufacture  are  not  made. 

Heat  treatment  is  the  basis  of  many  operations  in  shops 
and  to  make  it  good  and  cheap  requires  more  than  the  mere 
burning  of  coal  or  oil.  The  cost  of  fuel  is  not  as  important 
as  is  the  question  of  what  can  be  derived  from  it;  and 
this  depends  on  how  the  fuel  is  utilized.  The  number  of  heat 
units  obtained  for  a  cent  does  not  determine  the  quantity 
or  the  quality  of  the  product  obtained  for  a  dollar,  any  more 
than  the  price  of  gasoline  determines  the  cost  per  ton-mile 
of  running  an  automobile.  If  furnaces  are  so  designed  as  to 
utilize  powdered  coal  to  the  best  advantage,  and  the  coal  dust 
is  economically  conveyed,  fed  and  regulated  at  the  furnace, 
leaving  no  residue  of  fine  particles  of  dust  on  the  work; 
and  if  the  smoke  and  ash  are  properly  carried  away;  this 
fuel  meets  all  reasonable  requirements.  Powdered  coal 
gives  a  better  and  softer  heat  than  any  other  fuel  in  use  at 
the  present  time. 

The  economy  of  powdered  coal  over  oil  is  established, 
and  is  probably  the  one  factor  that  is  mainly  responsible 
for  the  present  active  interest  in  its  application.  Systems 
have  been  installed  to  replace  oil  where  there  has  been  an 
actual  saving  of  60  per  cent.  This  is  certainly  worth  while. 
As  compared  with  producer  gas  plants,  the  manufacturers 
of  the  latter  apparatus  bring  forward  many  arguments  in 
its  favor;  but  with  an  initial  loss  of  20  per  cent  or  more  in 
the  process  of  manufacture  of  gas,  there  is  every  reason  to 

09 


100 


POWDERED  COAL  AS  A  FUEL 


POWDERED  COAL  IN  METALLUGRICAL  FURNACES     101 

believe  that  powdered  coal  has  the  advantage.  Here 
every  unit  of  heat  is  projected  into  the  furnace:  and  in  the 
furnaces,  it  is  expected,  equal  efficiencies  will  be  realized 
from  powdered  fuel  and  gas.  Producer  gas  has  its  place 
where  checker  work  and  ash  troubles  are  objectionable. 
Where  the  ash  can  be  taken  care  of,  there  seems  to  be 
a  saving  by  the  use  of  coal  amounting  to  about  25  per  cent. 

Some  manufacturers  of  powdered  coal  installations  argue 
that  the  proper  way  to  measure  efficiency  is  on  a  B.t.u. 
basis.  In  other  words,  if  a  furnace  performing  a  certain 
heating  operation  uses  20  gallons  of  fuel  oil  per  hour,  each 
gallon  of  oil  containing  140,000  B.t.u.,  there  will  be  con- 
sumed 2,800,000  B.t.u.  in  the  operation.  On  this  basis, 
it  will  require  2,800,000  B.t.u.  in  coal  in  a  pulverized  state 
to  perform  the  same  operation,  the  superior  efficiency  of 
coal  arising  from  the  fact  that  the  2,800,000  B.t.u.  in  oil 
would  cost  more  than  the  same  number  of  B.t.u.  in  coal. 
This  fact  is  obvious;  for  if  fuel  oil  costs  5  cents  a  gallon, 
coal  (at  14,000  B.t.u.  per  pound)  would  have  to  be  sold  at 
$10  a  ton  to  give  an  equivalent  cost  per  B.t.u. 

But  this  comparison  does  not  by  any  means  measure  the 
efficiencies  of  heating  furnaces,  for  the  real  problem  is  one 
of  heating  cost  and  not  of  fuel  cost.  Powdered  coal,  or  any 
other  fuel,  in  substitution  for  what  is  now  in  use,  should  not 
be  chosen  for  the  mere  reason  that  it  has  a  lower  B.t.u. 
cost;  but,  rather,  one  must  select  a  fuel  which,  all  things 
considered,  will  show  the  lowest  production  cost  under  exist- 
ing conditions  in  the  shop. 

Production  costs  depend  on  three  things;  the  input, 
the  output  and  the  operator;  and  in  no  two  shops  are  these 
three  conditions  similar.  Each  shop,  on  account  of  its  con- 
ditions, requires  a  separate  study  to  determine  what  will 
lead  to  highest  efficiency  in  heating  operations. 

In  order  to  determine  the  efficiency  with  a  new  fuel  in 
comparison  with  a  fuel  now  in  use,  the  following  observa- 
tions should  be  made: 

Start  the  furnace  at  the  temperature  of  the  room,  raise 


102  POWDERED  COAL  AS  A  FUEL 

it  to  a  certain  final  temperature  and  note  the  time  taken 
for  this  operation,  both  with  the  fuel  now  in  use  and  with  the 
new  fuel  contemplated. 

Then  take  the  furnace  at  the  temperature  of  the  room 
and  put  in  a  certain  amount  of  material  at  the  same  tem- 
perature as  the  furnace;  and  raise  both  the  furnace  and  the 
material  to  a  certain  final  temperature,  noting  the  time  con- 
sumed in  this  operation,  for  each  of  the  two  fuels  in  question. 

Lastly,  start  the  furnace  and  material,  at  the  temperature 
of  the  room  (or  at  any  desired  temperature),  and  operate  the 
furnace  in  the  regular  manner.  Note  how  many  pounds 
of  material  are  raised  to  a  certain  final  temperature,  with 
the  number  of  pounds  of  coal,  oil  or  gas  expanded,  in  order 
to  perform  this  operation.  Unless  the  new  fuel  shows 
better  results  in  these  respects  than  the  fuel  formerly  used, 
it  is  not  more  efficient,  notwithstanding  arguments  by  the 
manufacturers  to  the  contrary.  If  powdered  coal,  tried 
out  in  this  manner,  does  not  produce  effects  superior  to  those 
from  fuels  formerly  used,  it  is  not  more  efficient. 

At  a  meeting  of  the  American  Institute  of  Mining  Engi- 
neers in  1913  Mr.  H.  R.  Barnhurst  presented  a  discussion 
from  which  the  following  is  abstracted.  The  proper  method 
of  firing  powdered  coal  is  to  admit  with  the  fuel  the  exact 
quantity  of  air  necessary  for  the  result  desired,  as  shown  by 
observation,  and  to  maintain  the  relationship  between  fuel 
and  air  as  long  as  the  conditions  desired  are  being  realized. 

This  matter  of  complete  control  of  the  two  factors,  fuel 
and  air,  is  and  will  be  at  the  root  of  all  success  with  pulver- 
ized or  sprayed  fuel  in  the  metallurgical  processes.  . 

It  is  unfortunate  that  in  the  present  state  of  our  arts  it  is 
difficult  to  obtain  exact  readings  of  the  temperatures  at- 
tained in  the  burning  of  fuel.  We  do  know,  however,  that  a 
definite  quantity  of  air  will  deliver  the  oxygen  required  to 
give  the  highest  attainable  temperature  from  a  given  fuel. 
With  a  knowledge  of  the  components  of  the  fuel,  the  laws 
of  thermo-chemistry  tell  us  not  only  the  quantity  of  oxygen 
we  must  have,  but  also  the  maximum  attainable  temperature. 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     103 

Applying  these  laws  further,  we  learn  that  any  air  or 
oxygen  supplied  in  excess  of  the  ideal  requirement  simply 
dilutes  the  products  of  combustion  and  lowers  the  tempera- 
ture; also,  that  insufficient  air  and  oxygen  will  cause  the 
burning  of  part  of  the  fuel  to  CO,  and  part  of  it  to  CCb. 
With  the  air  supply  halved,  we  obtain  only  the  poisonous 
and  inflammable  CO.  However  short  we  may  be  of  pyrom- 
eters, there  is  in  the  eye  of  the  intelligent  operator  a  gauge 
which  tells  him  at  a  glance  whether  the  heat  he  has  is  serv- 
ing his  purpose.  Pulverized  coal  is  at  a  great  advantage 
in  this  respect. 

It  need  not  be  supposed  that  an  operator  must  be  per- 
petually adjusting  his  apparatus.  If  we  find  that  with 
the  air  gate  fixed  at  a  certain  opening  the  fire  is  too  hot, 
a  simple  reduction  in  the  quantity  of  fuel  admitted  changes 
the  ratio  of  air  to  fuel  and  lessens  the  supply  of  heat.  If  the 
fire  is  not  hot  enough,  more  fuel  gives  more  heat  units  and 
a  lessened  excess  of  air,  resulting  in  a  heightened  tempera- 
ture. 

In  all  probability,  some  excess  of  air  must  always  be 
admitted  to  keep  the  temperature  from  reaching  destructive 
limits.  With  control  of  both  the  quantity  and  quality  of 
heat,  this  danger  is  negligible. 

The  temperatures  used  in  metallurgical  work  usually 
cover  a  range  of  nearly  2000°,  or  say  from  2000  to  4000°  F. 
By  ordinary  manipulation  as  described,  the  temperature  and 
quantity  of  fire  can  be  changed  as  easily  as  a  gas  jet  can  be 
turned  on  or  off.  The  response  is  instantaneous.  This 
particular  feature  renders  the  use  of  pulverized  fuel  par- 
ticularly suitable  for  metallurgical  furnaces.  Powdered 
coal  is  used  in  all  kinds  of  steel  and  iron  working,  including 
ore-roasting  and  flue-dust  nodulizing,  and  in  open-hearth 
furnaces,  puddling  furnaces,  busheling  furnaces,  heating 
furnaces  and  forge  furnaces. 

The  main  difficulties  in  the  earlier  and  experimental  stages 
were  caused  by:  1,  not  drying  the  coal;  2,  poor  pulveriza- 
tion; 3,  the  carrying  of  too  high  temperatures;  4,  the  use  of 


104  POWDERED  COAL  AS  A  FUEL 

passages  that  were  too  small,  giving  the  gases  too  high  a 
velocity. 

With  a  knowledge  of  how  much  air  must  be  supplied 
with  a  given  amount  of  fuel  to  produce  a  desired  temperature, 
and  a  knowledge  of  the  volume  of  the  gases  so  produced,  it 
is  easy  to  proportion  the  ports  both  of  inlet  and  outlet 
so  that  a  scouring  blowpipe  effect  may  be  avoided.  The 
excellent  practice  already  attained  is  undoubtedly  due  to  the 
application  of  such  knowledge. 

Aside  from  the  advantages  from  the  higher  efficiency 
attainable  with  this  fuel,  there  are  a  number  of  incidental 
factors  which  in  actual  service  contribute  to  the  profitable- 
ness of  its  use. 

The  furnace  begins  its  work  almost  instantly  and  with 
whatever  degree  of  temperature  intensity  may  be  desired. 
There  are  no  periods  of  lowered  temperature  due  to  firing 
cold  fuel.  There  is  no  cleansing  of  fires  for  puddling  or 
heating,  so  that  operation  is  practically  continuous.  There 
is  some  cinder  formed  in  puddling  and  heating  furnaces: 
this  is  disposed  of  in  the  usual  way.  Most  of  the  ash 
passes  out  of  the  chimney  and  floats  away  lightly.  A 
neutral  ash  content  within  reasonable  limits  does  not 
appreciably  affect  the  fire. 

It  has  been  somewhat  difficult  to  obtain  from  large  users 
exact  data  concerning  the  performance  of  the  various  fur- 
naces. Perhaps  the  best  evidence  of  success  is  the  contin- 
uance of  use  and  the  enlargement  of  plants  now  in  opera- 
tion. The  following  are  authentic  data:  In  roasting 
carbonate  ores  of  high  sulphur  content,  the  carbon  has  been 
driven  off  and  the  sulphur  reduced  within  permissible  limits 
by  the  use  of  fuel  amounting  to  less  than  7.5  per  cent  of  the 
weight  of  the  charge.  This  problem  involves  the  main- 
tenance of  a  low  temperature,  about  2100°  F.,  to  prevent 
the  agglomeration  of  the  ore  fines  into  masses.  The  same 
practice  obtains  in  the  roasting  and  nodulizing  of  ores 
and  flue  dust,  where  the  temperature  must  be  sufficient 
to  permit  the  ore  to  form  nodules  or  balls,  but  must  not 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     105 

be  so  high  as  to  cause  it  to  stick  to  the  walls  of  the  roasting 
kiln. 

In  open-hearth  practice  with  pulverized  coal,  steel  is 
usually  made  with  this  fuel  at  the  rate  of  from  450  to  500  Ib. 
of  coal  per  net  ton  of  product.  This  is  from  an  average 
of  45  heats,  the  fuel  and  product  being  carefully  weighed. 
These  figures  were  obtained  during  a  continuous  run  of 
six  weeks.  The  furnace  was  operating  beautifully  when 
visited  and  no  mechanical  difficulty  had  been  experienced. 
The  melts  were  obtained  in  slightly  less  time  than  with  oil. 

In  puddling  furnaces,  the  fuel  supply  varies  with  the 
season,  the  cool  weather  of  spring  and  fall  permitting  a 
larger  putput  than  when  intensely  hot  weather  affects  the 
men  at  the  furnace.  It  is  safe  to  say  that  iron  can  be  pud- 
dled at  an  average  expense  of  1200  Ib.  of  powdered  coal  per 
gross  ton  of  muck  bar  produced;  in  fact,  less  than  1000  Ib. 
of  coal  per  gross  ton  of  bars  has  been  shown  in  practice 
during  periods  when  favorable  temperatures  and  continuity 
of  work  conduced  to  high  economy. 

In  heating  furnaces  and  busheling  furnaces  there  is  some 
latitude  of  performance,  due  to  variation  in  charges  placed 
in  the  furnaces  and  in  the  sizes  of  mills  served  by  them. 
The  average  consumption  of  powdered  coal  in  heating 
furnaces  seems  to  be  from  500  to  550  Ib.  of  fuel  per  gross 
ton.  The  busheling  furnaces  require  from  550  to  600  Ib. 
To  obtain  such  results,  however,  the  furnaces  must  be 
properly  proportioned  and  equipped  and  in  good  condition. 
It  must  not  be  expected  that  the  results  obtained  by  simply 
squirting  coal  of  greater  or  less  degree  of  pulverization  into 
a  furnace,  with  an  unmeasured  jet  of  air,  will  equal  the  prac- 
tice here  shown.  Success  implies  dry  coal,  fine  pulveriza- 
tion and  proper  air  supply.  Another  factor  is  that  the  at- 
tendants should  be  interested  in  the  production  of  good 
results.  Men  of  good  order  of  intelligence,  operating 
mechanisms  which  displace  the  shoveler  and  the  wheel- 
barrow man,  and  who  are  constantly  on  the  "  firing  line  " 
both  practically  and  metaphorically,  are  extremely  valuable. 


106 


POWDERED  COAL  AS  A  FUEL 


POWDERED   COAL  IN  METALLURGICAL  FURNACES     107 

The  operations,  however,  are  simple  and  the  manipulations 
few  and  rational  in  their  nature.  With  such  men  further 
advances  in  economy  may  surely  by  looked  for. 

The  procedure  followed  in  the  proper  preparation  of 
powdered  coal  as  well  as  in  delivering  it  into  the  furnace, 
is  as  follows  (see  Chapter  III) : 

The  coal  is  received  in  the  pit  of  an  elevator,  into  which 
it  is  dumped  from  the  cars.  The  elevator  carries  it  to  the 
hopper  of  a  pair  of  crushing  rolls.  After  passing  through 
these  rolls  the  coal  may  be  weighed  by  automatic  recording 
scales  and  is  sometimes  caused  to  pass  over  a  magnetic 
separator.  The  coal  is  next  introduced  into  a  drier  to  expel 
the  moisture.  A  good  drier  of  approved  design  will  remove 
6  Ib.  of  moisture  per  pound  of  fuel  used  in  firing  the  drier 
and  the  product  will  ordinarily  carry  less  than  1  per  cent  of 
moisture.  From  the  pit  into  which  the  dried  coal  falls 
from  the  drier,  it  is  elevated  to  bins  above,  from  which  it  is 
evenly  fed  by  spouts  and  feeders  to  the  pulverizing  mills. 
These  mills,  if  of  proper  construction,  grind  the  coal  rapidly 
to  the  degrees  of  fineness  required. 

The  pulverized  coal  is  led  to  the  pit  of  an  elevator,  which 
carries  it  aloft  to  a  conveyor  which  distributes  it  to  the  coal 
bins,  from  which  it  is  delivered  by  gravity  to  pipes  leading 
to  the  burners. 

The  bins  for  holding  the  coal  are  proportioned  to  carry 
sufficient  fuel  to  serve  the  furnace  during  intervals  in  which 
the  mills  may  not  run;  as  for  instance,  coal  may  be  ground 
and  stored  for  twenty-four  hours  continuous  service  by 
running  the  mills  for  ten  hours. 

The  coal  is  fed  from  the  bottom  of  the  bin  by  a  worm 
feed-screw  provided  with  a  variable-speed  drive,  so  that  the 
furnace  may  receive  fuel  as  desired.  The  coal  falls  freely 
from  the  feed-screw  delivery  through  a  closed  pipe,  mixing 
with  the  air  in  its  descent  in  preparation  for  entering  the 
burner  pipe. 

The  burner  pipe  is  so  formed  that  the  air  passing  through 
it  from  a  fan  not  only  projects  the  fuel  into  the  furnace, 


108 


POWDERED  COAL  AS  A  FUEL 


FIGS.  31  and  32.— Fuller  Pulverized  Coal  Plant. 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     109 

but  also,  while  doing  this,  acts  as  an  injector,  drawing  with 
it  the  descending  column  of  air  containing  the  entrained 
coal  from  the  bins  above.  The  fuel  is  therefore  completely 
mixed  with  the  ultimate  column  of  air  while  entering  the 
furnace.  The  speed  and  volume  necessary  for  proper  fur- 
nace performance  are  predetermined  from  known  data. 

The  air  is  controlled  by  the  fan  speed  or  by  gates,  or  by 
both,  and  the  coal  by  the  number  of  revolutions  of  the  feed 
screw  per  minute.  The  operator  adjusts  these  factors  to  the 
quantity  and  intensity  of  fire  desired,  and  by  inspection  at 
times  sees  that  the  conditions  remain  as  required.  The 
construction  of  the  furnace  is  not  materially  changed  when 
powdered  coal  replaces  oil  or  gas.  The  operating  cost  in 
the  furnace  room  is  very  low,  as  one  man  can  oversee  a  num- 
ber of  furnaces.  The  furnaces  are  so  varied  in  construc- 
tion and  operation  that  it  would  not  be  possible  to  describe 
all  of  them  (see  Chapter  IV).  It  may  suffice  to  state  that 
any  solid  fuel  which  can  be  dried  and  pulverized  will  reach 
its  highest  efficiency  in  that  form,  and  for  this  reason  fuels 
hitherto  deemed  unavailable,  such  as  coke  breeze,  lignite 
culm,  and  anthracite  culm,  may  be  now  looked  to  for  a 
cheap  source  of  heat. 

In  actual  practice  in  the  use  of  powdered  coal,  the  ease 
with  which  it  is  burned  has  been  to  a  certain  extent  a  draw- 
back rather  than  an  advantage.  The  novelty  of  the  method 
is  so  attractive  that  those  experimenting  with  it  are  at  first 
satisfied  with  producing  a  good  fire  with  simple  apparatus 
in  which  may  exist  no  such  means  of  control  as  are  necessary 
for  realization  of  the  highest  economy. 

It  is  no  success  to  use  twice  as  much  fuel  as  the  work  may 
require,  nor  is  it  a  success  to  drive  a  small  fire  to  a  destructive 
intensity  in  order  to  offset  defective  proportioning  in  design. 
Correct  proportioning  involves  knowledge  of  the  heat  re- 
quirements of  the  job.  The  amount  of  fuel  necessary  may 
be  ascertained  and  the  volume  and  velocity  of  the  air  supply 
computed.  With  this  comes  necessarily  a  prescription  of 
the  volume  of  the  furnace,  so  that  combustion  may  have 


110 


POWDERED  COAL  AS  A  FUEL 


time  for  its  completion.  The  proper  size  of  ports  taking  off 
the  gases,  the  size  of  the  chimney,  and  the  velocities  of  the 
gases,  should  all  be  as  carefully  determined  for  powdered 


coal  as  for  gas  or  oil.     A  simple  experiment  based  on  one 
set  of  conditions  should  not  be  regarded  as  conclusive. 

With  proper  proportioning  of  the  apparatus,  the  opera- 
tion will  be  elastic  and  adjustable  to  a  wide  range  of  perform- 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     111 

ance  under  a  very  nearly  constant  percentage  of  efficiency. 
This  is  unattainable  in  an  installation  not  proportioned  for 
high  efficiency.  The  ease  with  which  powdered  coal  is 
burned  is  no  assurance  that  the  best  results  are  being 
obtained. 

METALLURGICAL    FURNACES    AT    THE    GENERAL    ELECTRIC 
COMPANY'S  WORKS 

The  General  Electric  Company  has  had  a  powdered  coal 
plant  at  its  Schenectady  works  for  the  past  five  years,  which 
has  been  visited  a  number  of  times  by  the  author.  The 
information  given  below  was  obtained  from  Mr.  A.  S. 
Mann,  who  had  charge  of  the  powdered  coal  installation, 
the  success  of  which  was  due  entirely  to  his  untiring  efforts. 
A  resume  of  Mr.  Mann's  conclusions  appeared  in  the  Gen- 
eral Electric  Review,  and  some  of  the  following  material  is 
quoted  therefrom. 

A  burner  which  was  perfected  by  Mr.  Mann  is  shown  in 
Fig.  34  to  36  inc.  This  consists  of  a  cast-iron  cylindrical 
box,  8  in.  in  diameter,  with  five  openings  beside  its  dis- 
charge mouth.  Either  of  the  openings  S  or  T  is  used  for 
coal  and  its  primary  air,  or  "  carrying  "  air  (40  to  60  cu.ft. 
per  pound  of  coal  dust).  Either  of  the  openings  X  or  Y  is 
used  for  the  combustion  air;  and  sometimes  air  is  admitted 
at  the  end,  at  U,  also.  The  first  four  of  these  openings 
are  tangential,  causing  the  air  currents  to  take  irregular 
spiral  forms,  and  they  are  used  for  short-burning  flames. 

For  an  ordinary  forge  furnace,  say  5  by  4  ft.,  S,  F,  and 
U  will  be  piped  up.  A  fire  is  started  by  using  combustion 
air  through  Y  alone,  for  through  its  use  a  short  complete 
mixture  can  be  dropped  right  upon  burning  kindling.  As 
long  as  this  arrangement  is  preserved  the  high  heat  will  be 
near  the  tuyere,  perhaps  12  in.  in  front  of  it.  It  sometimes 
happens  that  with  short  work  it  is  not  necessary  that  a  fur- 
nace be  hot  all  over  and  fuel  will  be  saved  if  there  be  a  high 
local  temperature  only.  If  a  complete  and  uniform  heat 
is  wanted  additional  combustion  air  is  admitted  at  U 


112 


POWDERED  COAL  AS  A  FUEL 


and  there  is  then  an  immediate  change  in  the  character  of 
the  fire.  The  flame  is  no  longer  local;  the  mixture  with  air 
is  not  as  good,  and  burning  calls  for  more  time.  Coal  that 


•AY 


^ 


13 


/7 


*>, 


A. 


8%D/A. 


FIGS.  34,  35  and  36. — Mann  Burner. 

can  find  adequate  air  near  the  tuyere  burns  there;  other 
coal  waits  till  it  finds  air,  and  there  is  a  long  flame  in  conse- 
quence. By  manipulating  the  air  valves  at  Y  and  J7,  the 


POWDERED   COAL  IN  METALLURGICAL  FURNACES     113 

range  of  regulation  is  great  and  it  is  possible  to  make  a 
very  long  flame;  even  as  much  as  30  ft.  long  under  certain 
conditions.  The  same  thing  is  true  of  an  oil  fire.  If  mix- 
tures are  very  poor  and  oil  is  sent  from  the  burner  in  slugs, 
a  flame  of  great  length  is  attainable;  it  is  only  requisite, 
for  a  long  flame,  that  the  fuel  and  air  travel  in  parallel 
streams,  whatever  the  nature  of  the  suspended  fuel.  Such 
long  flames  are  not  economical;  good  mixtures  give  good 
economy.  It  must  be  remembered  that  the  velocity  of  the 
stream  passing  along  the  axis  of  the  burner  should  not  be  so 
low  as  to  drop  the  coal.  The  burner  must  therefore  not  be 
too  large,  if  a  short  fire  is  wanted.  When  two  air  streams 
(as  at  S  and  F),  rotating  in  counter  directions,  meet,  rota- 
tion becomes  nil  and  the  axial  speed  must  be  enough  to  keep 
the  coal  in  suspension  and  preserve  the  mixture  already 
made.  It  will  be  noted  that  the  rotary  motion  within  this 
burner  is  just  the  motion  used  in  a  centrifugal  separator 
to  draw  moisture  out  of  steam,  or  in  a  dust  collector  to  sepa- 
rate air  from  solids.  In  these  devices  either  the  body  diam- 
eter is  large  enough  to  keep  the  two  elements  apart,  or 
baffles  are  provided  to  trip  the  heavy  material.  More- 
over, there  are  separate  and  guarded  outlets  for  the  two 
components  in  such  devices;  none  of  which  is  used  in  this 
burner.  That  the  device  does  produce  a  mixture  is  shown 
in  its  operation;  for  even  when  the  openings  S  .and  Y  are 
used,  causing  both  jets  of  air  to  swirl  in  the  same  direction, 
the  flame  is  only  about  24  in.  long.  As  the  combustion  air 
at  X  is  reduced  and  the  air  at  U  is  increased,  the  flame  length 
is  increased  and  combustion  becomes  slower,  showing  a 
less  perfect  mixture.  Some  of  the  furnaces  are  piped  in  just 
that  way;  and  though  the  range  is  not  great  it  is  ample  for 
most  forging  work. 

For  a  feeder,  the  General  Electric  Co.  has  found  that  a 
simple  screw  will  answer  every  purpose.  The  feeder  draws 
coal  from  a  supply  tank  and  delivers  it  in  definite  amounts 
to  a  cavity  from  which  it  can  be  picked  up  by  the  primary 
air,  which  carries  the  fuel  along  with  it.  In  this  plant  the 


114  POWDERED  COAL  AS  A  FUEL 

feeder  is  driven  by  a  small  motor  which  can  turn  at  1800 
r.p.m.,  800  r.p.m.  or  any  intermediate  speed.  It  is  geared 
down  only  once.  The  screw  will  feed  at  300  or  600  turns 
a  minute,  or  at  an  even  higher  speed  if  required.  With  so 
wide  a  speed  control  it  is  possible  to  carry  a  fire  that  shows 
just  a  visible  red;  by  a  simple  movement  of  a  rheostat 
handle  the  same  fire  will  spring  up  vigorously  and  shortly 
give  heat  enough  for  any  forge  work. 

There  is  a  feature  of  the  plain  screw-feed  that  makes  it 
very  convenient  in  many  situations,  viz. :  it  can  stand  a  little 
back  pressure;  so  that  the  discharge  distances  may  be  long. 

In  this  installation  the  coal  is  fed  across  the  shop  under- 
ground; the  supply  tank  with  its  feeders  and  motors  is  above 
ground.  The  coal  is  carried  90  ft.  or  more,  then  up  to  a 
furnace  and  its  burner.  The  distance  could  be  greater,  even 
several  hundred  feet,  and  the  control  would  be  just  as  conven- 
ient and  exact,  because  the  switch  and  rheostat  are  located  at 
the  side  of  the  furnace  and  the  operator  has  no  occasion 
to  come  over  to  the  supply  tank.  In  all  of  these  long  trans- 
missions there  will  be  a  little  back  pressure  at  the  screw. 
Primary  air  is  introduced  on  the  eductive  principle,  using 
the  fitting  shown  in  Fig.  37.  The  resistances  on  the  dis- 
charge side  increase  with  the  distance.  If  the  distance 
is  short,  there  is  a  negative  pressure  in  the  pipe  leading  from 
the  screw  to  the  opening  A  (see  Fig.  38).  Eight  inches  of 
vacuum,  by  water  column,  is  easily  attainable.  As  the 
discharge  distance  increases,  with  the  addition  of  elbows 
and  crooks,  this  vacuum  falls;  it  may  totally  disappear, 
and  there  may  exist  as  much  as  4  or  5  in.  of  pressure.  A 
plain  screw  is  little  affected  by  these  changes,  for  the  throat 
fit  at  A,  Fig.  38,  is  machined  so  that  a  certain  impetus 
is  given  to  the  coal.  The  long  distance  transmission  has  been 
so  proportioned,  however,  that  the  static  pressure  is  usually 
negative,  say  1  in.  or  so  of  vacuum. 

The  feeder  box  and  the  screw  are  shown  in  Fig.  39  and 
Fig.  40  respectively.  While  usually  only  a  small  amount 
of  power  is  needed  to  turn  the  screw  (it  can  be  turned  with 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     115 


FIG.  37. — Fitting  for  Introducing  Primary  Air 


g 

£  % 


THESE  F/TS  AKE  BASB/TT-SO. 


-/6*f 


a 


Jl 


FIG.  38. — Feeder  Box — Longitudinal  Section.  FIG.  39. — Feeder  Box— Cross  Section, 


FIG.  40.— Feeder  Box  Screw. 


116  POWDERED  COAL  AS  A  FUEL 

the  finger  fast  enough  to  carry  a  moderate  fire)  there  are 
times  when  a  considerable  amount  of  power  is  required. 
Normally  the  coal  is  light  and  fluffy,  but  under  certain 
conditions  (as  after  long  standing)  coal  packs  so  tightly 
that  no  mechanical  device  can  move  it.  The  screw  is  cut 
in  a  lathe  with  spaces  proportioned  to  the  quantity  required. 
A  2J-in.  diameter  screw,  as  shown,  will  feed  700  Ib.  per  hour, 
and  with  slight  modifications  much  more.  The  bottom  of 
the  thread  is  tapered  so  that,  after  the  screw  has  "  taken  its 
bite,"  the  volume  increases  as  the  threadful  advances,  and 
the  flow  to  the  pipe  is  free  and  easy  in  consequence.  The 
weight  of  a  cubic  foot  of  powdered  coal  may  be  anything 
from  29  Ib.  to  50  Ib.  When  delivered  by  a  conveyor  screw 
to  a  tank  7  ft.  deep  and  then  measured  immediately,  it  weighs 
31f  Ib.  per  cubic  foot.  In  twenty-four  hours  it  will  reach 
35  Ib.  and  it  then  increases  in  density  until  within  six  weeks 
(without  jarring)  it  will  weigh  38 J  Ib.  These  changes  will 
take  place  in  a  container  with  smooth  sides  with  a  diameter 
equal  to  half  its  depth.  In  a  piece  of  6-in.  vertical  pipe 
10  ft.  6  in.  long,  it  was  found  that  there  was  little  settlement 
even  after  two  months.  The  weight  of  coal  in  the  tanks  is 
computed  at  35  Ib.  per  cubic  foot.  Sometimes  the  coal 
flows  as  freely  as  a  liquid  and  will  spread  out  so  that  its 
top  surface  is  nearly  level  in  the  tank.  At  other  times  it 
will  not  even  flow  down  hill,  though  it  always  moves  freely 
enough  unless  it  has  been  stopped  for  forty-eight  hours  or 
longer. 

This  tendency  to  pack  and  clog  is  due  to  the  physical 
arrangement  of  the  particles  through  settlement  rather  than 
to  moisture.  Powdered  coal  will  absorb  microscopic  par- 
ticles of  water,  but  it  cannot  be  made  wet  by  throwing 
water  upon  it.  It  is  impossible  to  make  a  paste  by  using 
sticks  to  stir  the  coal  into  water.  The  only  way  to  make  a 
mixture  is  to  take  a  little  coal  and  water  between  the 
finger  and  thumb  and  knead  the  two  together.  In  a  day 
or  so  this  water  evaporates,  leaving  the  coal  clean  and  dry. 

It  is  not  difficult  to  dry  the  coal  to  f  of  1  per  cent  of 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     117 

moisture  or  less,  but  there  is  always  some  small  portion 
that  contains  moisture  in  excess.  It  is  surprising  to  find 
an  8-ton  bin  of  coal  that  has  been  nicely  dried  dripping 
with  water  twelve  hours  afterwards;  but  it  does  so,  and  it 
is  not  an  uncommon  thing  to  find  a  pulverizer  frozen  up  with 
water  in  the  morning.  The  source  of  such  water  is  not 
hard  to  find.  When  coal  is  in  a  dryer  it  is  hot  and  so  is  the 
contained  air.  The  air  is  saturated  with  moisture  at  the 
temperature  of  the  dryer  and  when  the  coal  and  air  cool 
the  moisture  is  precipitated,  and  in  cold  weather  makes 
its  presence  felt.  It  thus  appears  that  coal  cannot  be  made 
thoroughly  dry  through  the  agency  of  high  temperature. 

It  is  often  asked  whether  an  oil  furnace  can  be  success- 
fully changed  over  to  use  powdered  coal.  This  has  been  done 
at  the  General  Electric  Company  works  in  the  following 
manner :  a  coal  furnace  needs  one  or  sometimes  two  burners, 
depending  upon  the  size  and  kind  of  work  that  it  is  doing. 
An  oil  fire  make  no  visible  smoke  and  there  is  little  or  no 
odor  from  its  products  of  combustion,  so  there  is  no  reason 
why  there  should  be  a  chimney  or  (in  many  cases)  even  a 
furnace  vent.  Flames  and  hot  gases  can  be  brought  up  to, 
and  passed  out  of,  the  door,  keeping  the  fronts  hot.  A 
coal  fire  yields  no  black  or  colored  smoke,  though  the 
gases  contain  some  small  particles  of  white  ash;  but  it 
does  have  a  decided  and  disagreeable  odor.  It  is  better 
then  to  provide  a  hood  over  the  furnace  door;  enveloping  it, 
if  heat  is  wanted  right  at  the  door  as  it  is  in  most  forge 
work;  and  this  hood  must  have  an  outdoor  vent.  If  all 
gases  are  allowed  to  escape  in  this  way,  the  heat  distribu- 
tion is  not  perfect,  and  therefore  it  is  best  to  use  a  chimney 
vent  at  an  appropriate  point.  It  is  good  practice  to  run 
this  chimney  up  through  the  roof  over  each  furnace  and  to 
cut  into  it  a  45°  Y  to  which  the  hood  vent  is  attached. 
An  upward  draft  is  induced  in  the  hood  vent  by  the  chimney 
draft.  Figs.  41  and  42  are  views  of  such  connections.  It 
pays  to  provide  a  nicely  fitted  damper  which  can  be  adjusted 
with  precision;  if  the  damper  works  on  a  screw  thread  the 


118 


POWDERED  COAL  AS  A  FUEL 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     119 

tips  can  be  moved  ^V  in.,  though  such  extremely  fine  adjust- 
ment is  not  usually  needed.  It  also  pays  to  preheat  the 
combustion  air.  The  saving  in  fuel  greatly  exceeds  that 
represented  by  the  heat  imparted  to  this  air.  It  was  found 


I 

fr— 

/P^T" 

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Hue                          r7ue 
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£>oor 

Door- 

FIGS.  43  and  44. — General  Electric  Co.  Powdered  Cbal  Furnace. 

that  a  saving  of  35  per  cent  was  secured  in  one  case  with 
air  preheated  to  334°  C.,  while  the  heat  added  to  the  com- 
bustion air  was  only  16  per  cent  of  that  in  the  coal.  Only 
a  moderate  air  temperature  was  used,  as  it  is  preferable  to 


120  POWDERED  COAL  AS  A  FUEL 

install  only  such  surface  as  can  be  readily  cleaned,  and  the 
low  temperature  prevents  the  burning-out  of  the  preheating 
surface.  It  is  good  practice  to  allow  15  sq.ft.  of  surface 
in  a  furnace  that  burns  100  Ib.  of  coal  per  hour,  with  an 
inside  temperature  of  1355°  C. 

The  preheater  is  made  of  3-in.  cast  iron  soil  pipe,  six 
lengths  being  rusted  into  a  header  at  either  end,  and  placed 
beneath  the  hearth  in  the  path  of  the  waste  gases. 

Two  vertical  sections  of  a  furnace  which  is  used  in  the 
General  Electric  works  are  shown  in  Figs.  43  and  44.  The 
hearth  is  43  in.  long  and  24  in.  deep,  though  this  same  design 
is  used  for  furnaces  having  twice  the  area. 

Furnace  Lining.  An  important  part  of  the  subject  of 
furnace  construction,  which  must  not  be  overlooked,  is  the 
durability  of  the  furnace.  In  the  metallurgical  arts,  when 
extreme  heat  is  a  feature  of  the  operation,  care  must  be 
taken  to  avoid  destroying  the  furnace  by  its  own  opera- 
tion. This  is  not  difficult.  Much  of  the  trouble  has  arisen 
from  the  gases  impinging  upon  the  furnace  walls  at  points 
where  changes  of  direction  of  gas  travel  are  necessary,  and 
from  too  high  a  velocity  of  gases,  due  to  contracted  areas 
for  passage. 

Powdered  coal  is  destructive  because  of  concentrated 
heat  of  blowpipe  tendency,  wearing  effect  due  to  the  im- 
pinging of  the  coal,  and  the  tendency  of  the  ash  and  brick 
to  flux  together.  These  objections  are  partially  overcome 
by  the  use  of  low  air  pressure,  introducing  the  coal  at 
a  very  low  velocity,  spreading  the  flame  over  as  large  an 
area  as  possible,  and  the  cooling  of  brickwork  by  water 
circulation.  Where  the  fuel  blows  against  a  bridge  wall, 
the  latter  requires  frequent  repair.  There  has  been  a  gradual 
reduction  of  air  pressures  from  20  Ib.  on  the  cement  fur- 
naces of  early  days  down  to  as  low  as  |  oz.  on  metallurgical 
furnaces.  This  drop  in  pressure  has  been  due  to  an  effort 
to  avoid  the  destructive  effect  of  the  heavy  blast  of  powder 
against  the  brickwork.  Where  low  pressure  is  used,  it 
must  be  applied  close  to  the  furnace,  for  4  oz.  of  pressure 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     121 

is  necessary  to  carry  the  fuel  through  even  a  short  length  of 
pipe. 

If  the  utilized  heat  is  largely  absorbed  from  the  gases  by 
the  charge,  the  waste  gases  will  be  proportionately  less 
active  in  scouring  the  brickwork.  In  almost  any  con- 
struction (except  perhaps  a  rotary  cement  kiln)  it  is  found 
necessary  to  change  the  direction  of  the  gases  in  their  prog- 
ress toward  the  flue.  This  change  of  direction  causes  the 
gases  to  impinge  upon  the  diverting  bricks  with  an  energy 
proportional  to  their  velocity.  The  brick  can  be  fully  pro- 
tected at  these  points  by  a  system  of  water-cooled  pipes 
imbedded  in  the  walls.  The  brick  may  fret  away  somewhat 
until  the  area  of  protection  is  reached,  after  which  further 
progress  is  arrested. 

The  surprisingly  small  amount  of  water  which  it  has  been 
found  necessary  to  introduce,  while  maintaining  the  outlet 
below  200°  F.,  proves  that  the  cooling  effect  is  limited  to  a 
prevention  of  cumulative  action  and  is  not  perceptably  a 
drawback  upon  efficiency.  Of  course,  the  piping  must  be  so 
arranged  that  no  air  or  steam  pockets  shall  exist  and  so  that 
the  circulation  will  be  proportional  to  the  heat  stimulus. 

At  the  General  Electric  works,  furnace  linings  have  occa- 
sionally been  burned  out  by  powdered  coal  fires.  Sometimes 
a  wall  looks  like  the  rocks  in  a  turbulent  stream  after  ages 
of  wearing.  The  brick  has  been  cut  away  in  a  few  weeks. 
Coal  may  be  destructive  in  its  action,  but  it  need  not  be. 
A  hot  stream  of  coal  and  air  driven  at  high  speed  against 
a  wall  will  cut  it  out.  A  low-fusing  point  brick  is  melted 
down;  a  refractory  brick  is  cut  away  mechanically.  It  is 
possible  to  cut  away  carborundum  brick  by  misdirecting  a 
fire  which  did  not  even  approach  in  temperature  the  melt- 
ing temperature  of  the  brick.  But  such  action  is  unnec- 
essary. Except  at  the  burning  tuyere,  brick  need  not  meet 
a  destructive  flame,  and  the  tuyere  itself  can  be  so  shaped 
that  repairs  will  be  minor  and  infrequent.  The  remedy 
for  melting  down  is  to  avoid  high  velocity  along  the  brick- 
work. If  a  wall  must  take  the  full  force  of  a  current, 


122  POWDERED  COAL  AS  A  FUEL 

it  is  best  to  protect  it  with  loose  brick  or  to  pass  a  current 
of  combustion  air  along  its  face,  which  both  deflects  and 
protects.  An  arch  can  always  be  treated  in  this  way. 
Some  of  the  combustion  air  is  cut  off  from  a  burner  and 
sent  along  on  top  and  over  it.  The  total  volume  of  air  used 
is  not  increased  and  a  reducing  fire  can  still  be  carried; 
the  heat  distribution  is  noticeably  good. 

An  interesting  problem  in  furnace  construction  presented 
itself  in  a  case  where  it  was  desired  to  heat  certain  metals 
very  slowly  and  uniformly;  the  furnace  to  be  charged  when 
cold,  that  is  at  room  temperature,  and  brought  up  to  900°  C. 
in  six  hours,  the  rate  of  temperature  rise  not  to  exceed  200°  C. 
per  hour  at  any  part  of  this  time.  After  reaching  900°  C. 
the  heat  was  to  be  held  for  the  rest  of  the  day.  Perhaps  this 
can  be  done  with  other  fuels;  it  was  very  easily  done  with 
powdered  coal,  and  there  would  have  been  no  trouble  in 
holding  to  a  temperature  increase  of  20°  per  hour  had  it  been 
required.  This  was  true  of  the  first  hour  too,  which,  by  the 
way,  presents  the  greatest  difficulty. 

It  may  be  of  interest  to  note  the  result  of  trials  upon  fur- 
naces built  to  heat  metals  for  forging  purposes.  There  is  no 
standard  of  comparison  as  there  is  in  the  case  of  a  boiler 
trial,  so  one  had  to  be  devised.  There  were  eleven  billets, 
4  in.  square  and  about  20  in.  long,  weighing  approximately 
91  Ib.  each,  which  were  to  be  melted  down  for  scrap.  The 
two  furnaces  selected  could  each  heat  one-half  of  them  at  a 
charge,  five  at  one  time  and  six  at  the  next,  so  the  hearth 
was  covered  over  50  per  cent  of  its  area  and  4  in.  deep. 
As  soon  as  six  of  these  billets  were  heated  to  a  smart  forging 
temperature,  just  short  of  dripping,  they  were  hauled  out  and 
the  five  cold  ones  put  in.  The  hot  billets  were  dropped  in  a 
tank  of  cold  water  and  kept  until  they  were  stone  cold. 
In  this  way,  these  charges  were  heated  alternately  all  day 
Fuel  was  weighed,  furnace  temperatures  were  measured, 
and  in  order  to  allow  for  the  metal  burned  away  it  was 
weighed,  at  the  beginning  and  close  of  the  trial,  to  give  an 
average.  The  procedure  in  boiler  testing  was  followed  as 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     123 


124 


POWDERED  COAL  AS  A  FUEL 


closely  as  possible,  with  these  two  differences — the  furnaces 
were  cold  when  started  and  not  all  the  metal  was  heated 
that  could  have  been  heated.  If  each  charge  had  been  twice 
as  great,  the  output  per  pound  of  fuel  and  the  working 
efficiency  would  have  been  nearly  twice  as  large;  for  only 
about  10  per  cent  of  the  fuel  in  the  furnace  goes  toward 
heating  the  charge;  one  quarter  of  the  rest  goes  to  heat  up 
the  brickwork,  and  the  balance  goes  up  the  chimney. 

The  table  below  gives  the  results  of  these  trials.  The 
first  was  upon  furnace  No.  4  with  cold  combustion  air  and 
coal  dust  for  fuel;  the  second  upon  No.  0  furnace  with  hot 
air  and  coal  dust;  the  third  was  with  oil  on  No.  0  furnace. 

RESULTS  OF  FORGE  FURNACE  TRIALS 


No.  4 
Furnace. 

No.  0 
Furnace. 

No.  0 
Furnace. 

Coal 

Coal 

Oil 

Duration  of  trial        .                

60  hr. 

60  hr 

60  hr 

Temperature  of  furnace  at  start  
Temperature  of  furnace  at  finish  
Average  furnace  temperature  
Time  per  heat,  including  warming  up    .  . 
Number  of  heats  

cold 
1370°  C. 
1300°  C. 
94  min. 
8 

cold 
1365°  C. 
1301°  C. 
85  min. 
10 

cold 
1350°  C. 
1270°  C. 
98  min. 
9 

Average  time  of  heat,  neglecting  first.  .  .  . 
Temperature  of  combustion  air 

51  min. 
16°  C 

41  min. 
334°  C 

44  min. 
240°  C 

B  t  u  per  pound  fuel  

14,000 

14,000 

19400 

Total  fuel  including  kindling 

1042  Ib. 

790  Ib 

518  Ib 

Total  steel  heated      

4288  Ib. 

5015  Ib. 

4563  Ib. 

Hourly  Quantities: 
Pounds  of  steel  per  hour.             

573 

659 

604 

Pounds  of  fuel  per  hour 

139 

104 

69  5 

Economic  results: 
Pounds  of  steel  per  pound  of  fuel  
B.t.u.  in  fuel  per  pound  of  steel  

4.11 
3406 

6.35 
2203 

8.83 
2196 

No.  4  furnace  is  somewhat  larger  in  area  than  No.  0.  The 
first  and  second  trials  may  be  compared  to  show  the  effect 
of  preheating  the  air;  the  second  and  third  to  show  the  rela- 
tive merits  of  coal  and  oil. 


POWDERED   COAL  IN  METALLURGICAL  FURNACES     125 

The  temperature  of  the  heated  air  was  apparently  higher 
in  the  case  of  the  coal  than  in  that  of  oil;  but  all  of  the  air 
was  preheated  for  oil;  while  primary  air,  or  say  25  per  cent 
of  the  total  air,  for  coal,  was  not  heated  at  all.  In  any 
event  the  same  air  heater  and  the  same  furnace  were  used 
in  the  two  cases. 

The  heats  in  this  class  of  work  are  unquestionably  better 
with  coal/  They  are  noticeably  brighter  and  softer;  to 
express  the  difference  as  a  forge  smith  would,  coal  heat  is 
more  penetrating,  and  in  a  given  furnace  more  work  can  be 
done,  and  more  fuel  can  be  well  burned,  with  coal  than  with 
oil.  Columns  No.  2  and  3  of  the  table  show  a  10-per  cent 
greater  output  with  coal  than  with  oil.  It  may  be  noted, 
however,  that  efficiencies  are  virtually  the  same.  The  same 
thing  is  true  in  comparing  coke  with  oil  in  a  large  oven, 
and  in  general  it  may  be  stated  that  efficiencies  will  be  equal 
if  the  fuels  are  properly  burned,  and  this  will  cover  coal  upon 
a  grate  too.  If  burning  conditions  are  right,  if  fires  are 
carefully  and  intelligently  watched,  efficiencies  will  be  high 
and  will  be  essentially  equal.  When  fires  are  not  under- 
stood, when  conditions  are  wrong  and  results  are  poor, 
there  is  no  use  in  trying  to  draw  conclusions  from  a  trial. 
The  speeds  of  two  race  horses  cannot  be  gauged  by  a  trial 
when  they  are  both  half  starved.  If  a  fire  beneath  a  boiler 
cannot  turn  75  per  cent  of  itself  into  steam — show  75  per 
cent  efficiency — either  the  operator  is  untrained  or  the 
burning  arrangements  are  wrong.  A  skillful  man  will 
obtain  better  than  75  per  cent. 

The  powdered  coal  furnace  has  no  ups  or  downs.  There 
is  no  thick  fire  or  thin  fire,  fresh  coal  or  old  coal  to  insure 
fluctuations.  The  furnace  can  always  be  kept  at  its  best 
working  point,  and  if  so  kept  it  will  be  heated  evenly  all 
over.  Of  course,  a  large  charge  of  metal  to  be  heated  will 
by  its  very  volume  absorb  heat  rapidly,  causing  a  fall  in 
waste  gas  temperature  and  possibly  a  little  smoke,  at  first. 
This  is  in  the  nature  of  things,  but  conditions  quickly  bring 
the  charge  to  a  point  where  the  chill  is  not  sufficient  to 


126  POWDERED  COAL  AS  A  FUEL 

affect  combustion.  High  temperatures  then  come  again 
and  smoke  disappears.  If  the  rate  of  work  to  be  done  is 
constant,  there  is  no  reason  why  high  efficiency  may  not  be 
uniformly  maintained  by  proper  construction  and  operation. 
The  subject  has  been  mastered  to  a  point  beyond  the  experi- 
mental stage.  High  efficiency  may  be  confidently  relied 
upon.  The  quality  of  the  coal  is  not  of  supreme  importance. 
Indeed,  in  the  developments  of  the  future  the  chief  attrac- 
tion of  powdered  coal  may  lie  in  high  efficiencies  obtainable 
from  low-class  or  refractory  fuels  hitherto  thought  unavail- 
able. 

AMERICAN   LOCOMOTIVE    CO.    PLANT 

At  the  works  of  the  American  Locomotive  Company  at 
Schenectady,  N.  Y.,  there  has  been  installed  one  of  the  pow- 
dered coal  plants  of  the  Quigley  Furnace  and  Foundry  Co. 
of  Springfield,  Mass.  This  has  been  visited  a  number  of 
times  by  the  author.  This  plant  works  very  satisfactorily 
with  a  distinct  saving  in  fuel  charges.  The  plant  formerly 
used  a  fuel-oil  system  for  heating  the  blanks  for  drop-forg- 
ings  and  for  general  small  forging  work. 

This  plant  was  built  and  started  in  May,  1913,  and  while 
there  has  been  the  usual  amount  of  trouble  to  be  expected 
in  starting  up  new  equipment,  the  system  is  at  the  present 
time  giving  good  results. 

The  coal  milling  and  distributing  plant  is  motor-driven 
and  centrally  located  in  a  building  of  non-combustible  con- 
struction. At  present  it  has  a  capacity  of  5  tons  per  hour, 
and  it  is  so  arranged  that  by  duplicating  the  dryer  and  pul- 
verizer its  capacity  can  be  doubled.  The  plant  has  a  con- 
crete hopper  placed  under  an  elevated  track  where  it  can 
be  served  with  coal  either  by  discharging  directly  into  it 
from  the  car  or  from  the  stock  pile  by  means  of  a  traveling 
crane  and  grab  bucket.  The  concrete  hopper  discharges 
into  a  rotary  crusher  capable  of  crushing  20  tons  per  hour 
of  run-of-mine  coal  to  f-in.  cubes,  from  which  the  coal  is 
carried  by  means  of  a  bucket  elevator  to  a  storage  bin  which 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     127 


128  POWDERED  COAL  AS  A  FUEL 

discharges  through  chutes  and  a  reciprocating  feeder  into  an 
indirect  dryer  of  6  tons  capacity  per  hour.  From  here  it 
is  elevated  to  a  dried-coal  storage  bin  arranged  to  feed  by 
chutes  directly  into  the  pulverizer,  then  elevated  to  a  pul- 
verized-coal  storage  bin,  from  which  it  is  distributed  by 
means  of  screw  conveyors  to  the  various  furnaces  in  the  drop- 
forge  shop.  The  plans  permit  of  further  extension  to  the 
blacksmith  shop  and  other  departments  later. 

The  milling  building  is  detached,  well  ventilated,  and 
well  built  in  conformity  with  underwriters'  requirements, 
and  has  been  accepted  by  them  as  on  a  par  with  buildings 
containing  equipment  for  fuel  oil  or  gas  for  industrial 
purposes.  There  has  been  no  trouble  whatever  from  spon- 
taneous combustion,  or  from  fires  from  other  causes,  and 
there  appears  to  be  no  reason  to  expect  trouble  from  this 
source  if  ordinary  precautions  are  used,  as  required  with  any 
other  kind  of  fuel. 

The  feed  device  used  at  the  American  Locomotive  shops 
has  a  motor-driven  controller  and  consists  mainly  of  two 
screws,  the  upper  located  so  as  to  propel  the  powdered  coal 
from  the  bin  forward  to  a  point  where  it  falls,  in  a  stream, 
past  an  opening  through  which  a  cross  current  of  air  at  low 
pressure  (a  small  portion  of  the  total  amount  of  the  air  re- 
quired for  combustion)  is  directed,  so  as  to  force  the  desired 
quantity  of  coal  to  the  burner  through  suitable  pipes. 
The  lower  or  return  screw  is  of  greater  pitch  than  the  upper 
and  returns  any  excess  of  coal  to  the  base  of  the  hopper. 
By  this  method  a  continuous  stream  of  coal  passes  the 
opening  and  any  portion  up  to  the  capacity  of  the  upper 
screw  may  be  utilized  by  increasing  or  decreasing  the  force 
of  the  cross  jet  of  air.  As  the  lower  screw  has  a  greater 
capacity  than  the  upper  it  is  impossible  to  clog  the  device 
even  when  the  consumption  of  coal  is  altogether  stopped. 

The  oil  was  measured  as  follows:  There  were  two  tanks 
with  gauge  glasses,  so  that  the  exact  level  of  oil  could  be 
determined:  the  tanks  were  so  connected  that  one  could 
be  filled  with  oil  while  the  other  supplied  oil  to  the  furnaces. 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     129 


TESTS  AT  AMERICAN  LOCOMOTIVE  COMPANY  WORKS 

Test  on  Oil  Furnace. 

Nov.  14,  1913.     Test  started  6:10  A.M.— ran  to  3:35  P.M. 

Furnace  ran  11  heats,  12  pieces  to  each  heat:  pedestal  die  wedges. 


Heats. 

Time,  Minutes. 

Forging  Time, 
Minutes. 

Pieces. 

1 

31 

18 

12 

2 

25 

18 

12 

3 

20 

16 

12 

4 

21 

19 

12 

5 

23 

18 

12 

6 

21 

17 

12 

7 

40 

22 

12 

8 

28 

16 

12 

9 

21 

16 

12 

10 

23 

17 

12 

11 

31 

16 

12 

Total  actual  time,  9  hours,  25  minutes. 

Oil  used,  1238  gallons. 

Blast  on  oil  burner,  6|  ounces  from  6-in.  pipe,  reduced  to  4  in.  at 
burner. 

Motor,  120  horse-power,  runs  three  No.  10  Sturtevant  blowers  for 
blast. 

Each  blast  consumed  1|  horse-power. 

COMPARISON  OF  POWDERED  COAL  FURNACE  AND  OIL 

FURNACE 

(Both  same  size) 


Powdered  Coal 
Furnace. 

Fuel  Oil  Furnace. 

Time  run 

10  hr.  22  min. 

9  hr  25  min 

Fuel  consumed 

2177  Ib  coal 

138  gal  oil 

Average  time  per  heat 

25  1  min 

25  8  min 

Average  time  per  forging  

1.87  min. 

1.47  min. 

Actual  forgings  

122 

132 

Forgings  to  be  counted  

132 

132 

Cost  of  fuel  at  contract  price  

$2.82  ($2.56 

$6.69  (4.8c. 

Cost  of  fuel  delivered  to  the  furnace  .  .  . 

per  ton) 
$3.31 

per  gal.) 

$6.89 

130  POWDERED  COAL  AS  A  FUEL 

The  tanks  were  accurately  calibrated  and  the  oil  consumption 
computed  accordingly. 

The  powdered  coal  furnace  ran  fifty-seven  minutes  longer 
than  the  oil  furnace.  However,  thirty  minutes  were  lost 
because  of  failure  to  charge  the  furnace  on  November  12 
and  eighteen  minutes  were  lost  on  November  13,  because  the 
plate  for  heating  the  dies  was  not  put  in  at  the  proper  time. 
The  work  was  on  pedestal  die  wedges,  which  are  of  iron. 
The  blocks  weigh  25  Ib.  and  the  forgings  16  Ib.  The  time 
lest  on  the  powdered  coal  furnace  would  have  been  more  than 
sufficient  for  making  ten  additional  forgings,  so  that  the 
amounts  turned  out  by  the  furnaces  should  be  considered 
equal,  as  indicated  in  the  table  above. 

Some  weight  should  be  given  the  fact  that  the  oil  costs 
were  probably  kept  at  a  minimum,  as  the  operator  was 
thoroughly  familiar  with  oil  and  was  able  to  obtain  the  maxi- 
mum heat  with  the  minimum  amount  of  fuel.  The  same  men 
ran  the  two  furnaces  and  the  only  variable  factor  of  impor- 
tance was  that  the  ram  used  on  the  hammer  at  the  oil  furnace 
was  about  500  Ib.  heavier  than  the  ram  on  the  hammer  at 
the  coal  furnace.  This  did  not  affect  the  time  of  heats,  but 
allowed  a  quicker  forging  time  and  there  was  therefore  less 
time  lost  with  nothing  in  the  furnace,  when  using  oil. 

AMERICAN   IRON   AND    STEEL   PLANTS 

The  Lebanon  plant  is  described  by  Mr.  James  Lord  in  the 
Western  Engineer's  Society  Proceedings.  About  1903,  the 
American  Iron  and  Steel  Company,  noting  the  use  of 
powdered  coal  in  large  furnaces  in  the  cement  industry, 
commenced  the  experimental  use  of  this  fuel  in  metallurgi- 
cal furnaces. 

From  the  first  it  was  apparent  that  economical  use  de- 
pended upon  absolute  control  of  the  feed  by  the  burner. 
This  having  been  accomplished,  the  fuel  has  been  applied 
to  over  one  hundred  furnaces  of  various  types,  such  as  those 
for  puddling  and  heating,  and  of  smaller  sizes  for  reheating 
nut,  bolt  and  spike  bars. 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     131 


132  POWDERED  COAL  AS  A  FUEL 

It  has  proved  to  be  a  commercial  success  for  all  of  the 
above  purposes  and  can  probably  be  used  with  equal  economy 
for  basic  open-hearth  steel  furnaces,  either  with  or  without 
checker  work.  Experience  in  the  use  of  this  fuel  over  a 
number  of  years  has  been  so  satisfactory  and  so  economical 
that  the  company  is  now  largely  increasing  its  installation, 
and  is  about  to  apply  it  to  open-hearth  furnaces. 

They  have  found  that  success  in  using  powdered  coal  for 
metallurgical  furnaces  requires: 

1.  That  both  the  free  and  combined  moisture  be  expelled 
by  artificial  heat,  down  to  about  0.5  per  cent. 

2.  That  the  coal  be  pulverized  so  that  95  per  cent  will 
pass  through  a  100-mesh  sieve,  and  over  80  per  cent  will 
pass  through  a  200-mesh  sieve. 

3.  That  delivery  to  the  furnace  be  controlled  by  the 
burner  so  that  the  proper  feed  may  be  secured.     The  capac- 
ities of  burners  used  at  Lebanon  range  from  40  Ib.  per  hour 
to  900  Ib. 

In  the  puddling  and  heating  furnaces,  the  firing  grates 
formerly  used  for  lump  coal  serve  as  combustion  chambers 
for  the  powdered  coal,  and  collect  a  large  portion  of  the 
ash.  The  combustion  chambers  in  the  heating  furnaces  hold 
about  6  tons  of  iron  piles,  and  are  about  5  ft.  from  back  to 
bridge  wall.  Some  ash  is  collected  at  the  base  of  the  stack, 
and  some,  of  impalpable  fineness,  passes  through  the  stack. 
That  which  falls  upon  the  material  in  the  furnace  is  too 
small  a  percentage  to  affect  it  unfavorably.  In  one  of  the 
plants,  located  near  a  residential  section,  suction  fans  have 
been  installed  to  collect  the  ash. 

The  equipment  for  preparation  of  the  powdered  coal  at 
the  Lebanon  plant  is  as  follows: 

The  slack  coal  is  conveyed  automatically  from  the  car 
to  the  pile,  then  taken  by  screw  conveyors  to  the  dryers, 
and  in  the  same  manner  from  the  dryers  to  the  pulverizers. 
When  ready  for  use  it  is  similarly  conveyed  throughout  the 
works,  in  some  cases  as  much  as  a  third  of  a  mile.  It  is  not 
touched  by  hand  or  shovel  from  the  freight  car  to  the  furnace. 


POWDERED   COAL  IN  METALLURGICAL  FURNACES     133 

Using  slack  coal,  a  crusher  is  unnecessary.  Various  types 
of  dryers  are  used.  The  pulverizers  are  of  two  types,  the 
horizontal  tube  mill,  and  the  upright  grinding  mill.  They 
are  practically  equal  in  efficiency,  each  machine  delivering 
4  to  4|  tons  per  hour.  Both  of  these  types  of  mill  are  made 
by  a  number  of  manufacturers. 

As  the  coal  leaves  the  pulverizing  plant  it  is  weighed 
on  a  large  automatic  scale.  The  heating  and  puddling 
furnaces  have  each  a  small  automatic  scale,  and  the  total  of 
the  small  scales  is  checked  up  each  day  with  the  large  scale. 

At  the  end  of  each  line  there  should  be  an  overflow 
pipe  to  prevent  the  coal  from  choking  up  the  screw,  if  any- 
thing should  happen  to  the  cross  lines.  Otherwise,  should 
the  coal  overflow  near  an  open  fire,  it  will  at  once  ignite. 

Attached  to  each  of  the  furnaces  is  a  tank  or  hopper,  of 
size  to  carry  about  a  fifteen-hours'  supply  of  powdered 
coal.  On  several  occasions  the  fuel  has  ignited  in  these 
tanks,  usually  on  Monday  mornings  when  the  left-over  coal 
had  accumulated  moisture.  In  such  cases,  it  is  only  neces- 
sary to  stop  the  supply  and  feed  the  burning  coal  into  the 
furnace  until  the  tank  is  empty.  There  is  no  danger  of  an 
explosion  under  these  conditions.  Indeed,  during  the  entire 
experience  at  the  Lebanon  works  with  this  fuel  there  have 
been  no  explosions.  These  occur  from  coal  in  suspension  in  a 
room  in  contact  with  flame.  The  same  result  would  follow 
filling  a  room  with  wheat  flour  in  suspension.  Proper  atten- 
tion to  the  pulverizing  plant  and  machinery  will  eliminate 
this  possible  danger. 

The  fuel  should  be  delivered  to  the  puddling  and  heating 
furnaces  at  a  low  air  pressure.  This  plant  employs  4  to  6  oz. 
of  blast  to  blow  the  coal  through  a  small  pipe  from  the  burner 
inlet  to  the  large  blast  pipe,  which  in  a  heating  furnace  is  from 
10  to  14  in.  in  diameter.  This  large  pipe  conveys  the  coal 
to  the  furnace  at  a  pressure  of  1  oz.  or  less  per  square  inch. 
If  these  pressures  are  adhered  to,  the  roof  and  side  walls  of  a 
furnace  heating  wrought  iron  for  the  rolling  mill  will  last  four 
or  five  months  when  running  double-turn,  six  days  per  week. 


134 


POWDERED  COAL  AS  A  FUEL 


As  to  the  economy  of  the  fuel,  actual  results  in  the  Cen- 
tral works  during  the  months  of  April  and  May,  1913,  are 
as  follows: 

Puddling  Furnaces.  The  following  figures  show  the 
quantity  of  fuel  consumed  to  produce  a  ton  of  puddled  bar, 
made  from  gray  forge  pig  iron.  (The  product  during  these 
months  was  high-grade  bar  requiring  special  work  and  time.) 


April,  Lb. 

May,  Lb. 

No.  23  furnace  .  .  '  

1362 

1318 

No.  24  furnace  

1109 

1277 

No.  25  furnace  

1271 

1472 

No.  26  furnace  

1371 

1362 

The  average  during  the  same  months  on  a  lower  grade  of 
pig  and  cast  scrap  was  1239  Ib. 

Heating  Furnaces.  In  heating  piles  for  rolling  the  fol- 
lowing results  were  obtained  during  the  same  months: 


Name  of  Mill. 

April,  Lb. 

May,  Lb. 

12-inch  Central 

516 

528 

12-inch  West 

544 

570 

16-inch  Central 

519 

533 

The  figures  show  the  weight  of  fuel  in  pounds,  consumed 
to  produce  a  gross  ton  of  rolled  bars.  On  steel  billets  the 
amount  would  be  one-third  less. 

Records  for  the  year  1912  show  the  cost  of  preparing 
pulverized  coal  to  have  been  as  follows: 

Rate  of  Gross  ton 
of  Coal  Powdered 

Fuel  for  dryer. $0.034 

Repairs  to  buildings 0 . 002 

Operation .  0 . 145 

Power  (steam  and  electric) 0.221 

Repairs  to  machinery  and  equipment 0 . 200 


Total $0.602 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     135 


136  POWDERED  COAL  AS  A  FUEL 

This  total  includes  the  cost  of  transmission  through 
pipes  to  the  furnaces. 

The  item  of  repairs  includes  expenses  which  should  have 
been  charged  over  the  past  eight  years,  and  the  total  cost 
of  preparation  and  transmission  did  not  actually  exceed  50 
cents  per  ton  of  powdered  coal  produced  during  1912. 

If  the  cost  of  transmission  is  separated  from  that  of  actual 
preparation,  the  cost  of  the  latter  would  be  less  than  40 
cents.  Many  plants  would  not  need  the  expensive  trans- 
mission system  required  at  Lebanon. 

In  general,  so  many  variable  quantities  enter  into  the 
matter  of  cost  that  one  can  hardly  set  an  exact  figure. 
At  the  same  time,  it  is  certainly  useless  to  accept  the  low 
figures  given  by  manufacturers  of  pulverizing  machines. 
We  hear  much  about  costs  of  10  or  12  cents  per  ton  for 
grinding,  which  may  be  adequate  for  some  part  of  the 
process.  What  the  purchaser  wishes  to  know  is  the  total 
cost  of  handling  the  coal  from  the  cars  up  to  the  furnace. 
The  very  extensive  and  well-designed  plant  at  Lebanon, 
from  exact  figures,  counts  on  50  cents  per  ton  for  unloading, 
screening,  drying,  grinding  and  placing  at  the  furnace. 
This  includes  the  wages  of  two  men  engaged  all  the  time  in 
unloading  cars  and  caring  for  the  distribution  of  the  coal. 
It  also  includes  the  care  of  the  dryer,  care  of  the  grinding 
plants  and  upkeep  of  the  apparatus.  This  50  cents  a  ton 
is  just  about  taken  care  of  by  the  difference  between  the  cost 
of  slack  coal  and  that  of  run-of-mine  coal,  the  latter  of  which 
could  be  used  on  ordinary  grate  fires. 

When  the  coal  is  prepared  as  herein  outlined,  smoke  is 
practically  eliminated.  If  the  stack  shows  black  smoke, 
it  proves  that  there  is  wasteful  use  of  the  fuel,  to  the  detri- 
ment of  the  operator's  interest,  and  this  is  or  should  be 
at  once  corrected. 

Fig.  45  shows  the  outline  of  a  furnace  from  which  gas 
samples  and  furnace  temperatures  were  taken  at  the  three 
points  indicated.  Gases  were  analyzed  by  an  Orsat  appa- 
ratus and  furnace  temperatures  were  taken  by  a  Thwing 


POWDERED  COAL  IN  METALLURGICAL  FURNACES     137 


radiation  pyrometer.  The  first  three  runs  were  made  under 
working  conditions,  heating  a  pipe  pile,  and  the  last  three 
with  the  furnace  empty.  The  coal  used  contained  54.86 
per  cent  fixed  carbon,  1.85  per  cent  sulphur,  0.74  per  cent 


FIG.  45. — Outline  of  Lebanon  Furnace. 

moisture,  32.68  per  cent  volatile  matter  and  11.72  per  cent 
ash.  Its  computed  heat  value  was  13,250  B.t.u.  per  pound. 
It  was  ground  so  that  89.07  per  cent  passed  over  a  100-mesh 
and  70.82  per  cent  over  a  200-mesh  screen. 


GAS  ANALYSIS. 

AIR  BLAST 
PRESSURE. 

Speed 

Air 

of 

Blast 

Date. 

Time. 

Bridge. 

Center. 

NearNeck. 

Control 

Pri- 

Sec- 

Temp. 

Screw 

rnary 

ondary 

Deg 

R.p.m. 

Blast. 

Blast. 

Fahr. 

C02 

0  CO 

C02 

0  CO 

C02 

0  CO 

(Oz.) 

(Oz.) 

10/14/14 

11:15  A.M. 

11.4 

3.6  0 

15.0 

2.1   0 

12.0 

2.8  0 

2:55  P.M. 

11.0 

6.0  0 

9.0 

0.7  0 

15.0 

1.7  0 

4:30  P.M. 

13.4 

2.6  0 

12.0 

4.0  0 

13.6 

4.6  0 

10/15/14 

4:10  P.M. 

13.4 

2.8  0 

13.0 

3.0  0 

12.8 

3.2  0 

54-62 

5.625 

0.625 

428 

4:50  P.M. 

11.4 

3.6  0 

12.2 

2.8  0 

9.2 

3.2  5 

37-42 

5.625 

0.500 

5:25  P.M. 

8.6 

5.4  0 

9.0 

4.0  0 

9.0 

4.6  0 

37-42 

5.625 

0.500 

STACK  AND  FURNACE  CONDITIONS 


BRIDGE. 

CENTER. 

NEAR  NECK. 

Test 
No. 

Smoke 
from 
Stack. 

Furnace. 

Temp. 
Deg.  F. 

Smoke 
from 
Stack. 

Furnace. 

Temp. 
Deg.  F. 

Smoke 
from 
Stack. 

Furnace. 

Temp. 
Deg.  F. 

1 

None 

Ready 

2560 

Trace 

Beginning 

None 

Drawing 

to  Draw 

to 

2 

None 

Drawing 



None 

Drawing 

None 

Making 

Bottom 

3 

Trace 

Ready 



None 

Ready 

None 

Drawing 

to  Draw 

to  Draw 

4 
5 
6 

Trace 
None 
None 

Empty 
Empty 
Empty 

2420 
2420 
2530 

None 
None 
None 

Empty 
Empty 
Empty 

2480 
2460 
2540 

None 
None 
None 

Empty 
Empty 
Empty 

2390 
2350 
2540 

CHAPTER  VIII 
POWDERED  COAL  UNDER  BOILERS 

A  PLANT  in  New  Jersey  recently  visited  by  the  author 
made  a  test  on  crushed  coal,  ground  to  a  fineness  of  only 
about  60  mesh.  The  coal  was  fed  into  a  "  coal  integrator  " 
and  conveyed  to  the  boiler  furnace,  a  distance  of  approxi- 
mately 100  ft.,  by  air  at  4  Ib.  pressure,  through  a  IJ-in. 
rubber  hose.  The  test  started  at  11  A.M.  with  the  furnace 
empty,  the  steam  gauge  then  showing  80  Ib.,  and  at  11:17 
A.M.  the  gauge  was  at  123  Ib.  and  the  safety  valve  blew. 
The  amount  of  coal  burned  during  this  time  was  470  Ib. 
and  the  amount  of  water  evaporated  about  9.5  barrels 
of  400  Ib.  each.  Then  (400x9.5)^-470=8.08  Ib.  of  water 
were  evaporated  per  pound  of  coal.  During  the  test  the 
coal  was  fed  through  the  top  of  the  furnace,  while  the  air 
for  combustion,  at  1-oz.  pressure,  was  fed  into  the  furnace 
from  both  sides  at  the  rate  of  180  cu.ft.  of  air  per  pound 
of  coal.  The  heat  was  so  concentrated  and  intense  that  the 
inside  lining  of  the  fire  box  door  was  melted.  Ash  piled 
up  in  the  furnace,  necessitating  a  shut-down  after  running 
about  an  hour,  for  cleaning  out.  The  trouble  was  no  doubt 
due  to  insufficient  grinding. 

Reference  was  made  in  Chapter  IV  to  the  apparatus 
devised  by  Whelpley  and  Storer,  for  firing  a  boiler  in  part 
with  powdered  coal.  This  was  experimented  with  at  an 
early  date  by  Chief  Engineer  B.  F.  Isherwood,  TJ.S.N. 
The  boiler  was  of  the  horizontal  type  with  two  flues,  having 
299  sq.ft.  of  heating  surface  and  13^  sq.ft.  of  grate.  A  coal 
fire  was  maintained  upon  the  grate  and  the  powdered  coal 
fed  in  above  it,  a  fire  arch  being  used  to  maintain  the  fur- 
nace temperature  when  the  powdered  coal  was  used,  but  not 
when  the  grate  fire  was  employed  alone. 

138 


POWDERED  COAL  UNDER  BOILERS 


139 


Figs.  47  to  49  show 
an  arrangement  of  ap- 
paratus for  burning 
powdered  coal  under  a 
Heine  boiler.  Most  of 
those  engaged  in  ex- 
perimental work  on 
powdered  coal  under 
boilers  have  ignored 
the  fact  that  a  com- 
bustion chamber  for 
burning  powdered  coal 
must  be  considerably 
larger  than  one  for 
burning  the  same 
quantity  of  coal  upon 
a  grate.  The  floor  of 
the  combustion  cham- 
ber in  this  instance 
consists  of  cinders 
thrown  upon  a  row  of 
water- tubes  A.  There 
is  a  wide  slot  in  the 
middle  of  this  floor, 
through  which  the 
liquid  ash  may  drop 
into  the  ash  pit,  which 
is  water-cooled.  The 
globules  of  liquid  ash 
take  on  a  skin  or  shell 
in  falling,  which  pre- 
vents the  formation  of 
a  lake  at  the  bottom 
of  the  ash  pit. 

The  combustion 
chamber  should  have 


140 


POWDERED  COAL  AS  A  FUEL 


FIGS.  47, 48  and  49.— Heine  Boilers  Arranged  for  Pulverized  Coal. 


POWDERED  COAL  UNDER  BOILERS 


141 


a  volume  of  about  1  cu.ft.  for  each  3  Ib.  of  coal  burned  per 
hour. 

In  Fig.  48,  B  are  water-tubes  which  protect  the  furnace 
walls  from  smelting;  C  is  the  bed  of  ashes,  or  floor  of  the  com- 
bustion chamber,  D  is  the  slot  through  which  the  liquid 
ash  may  drip,  E  are  the  headers  and  F  are  the  tuyeres. 

The  ash  pit  should  be  3  ft.  deep  to  allow  the  liquid  ash 
to  cool  while  falling.  All  joints  should  be  protected  from  the 
direct  action  of  the  flames. 

At  the  1914  spring  meeting  of  the  A.S.M.E.,  Mr.  F.  R. 
Low  presented  a  paper  entitled  "  Pulverized  Coal  for  Steam- 
Making  "  which  described  the  following  forms  of  apparatus 
used  for  powdered  coal. 

There  have  been  three  general  types  of  apparatus  pro- 
duced: Fig.  50  shows  the  Pinther,  in  which  the  powdered 


FIG.  50. — Pinther  Apparatus. 

coal  is  emptied  into  a  hopper  above  a  feed-controlling 
mechanism  and  is  then  carried  into  a  furnace  by  natural 
draft;  the  second  type  is  that  having  a  mechanical  feed, 


142 


POWDERED  COAL  AS  A  FUEL 


like  the  revolving  brush  of  the  Schwartzkopf  apparatus, 
Fig.  51;  and  the  third  form  is  that  in  which  the  coal  is 
blown  into  the  furnace,  as  in  the  Day  or  Ideal  apparatus. 

With  the  first  type,  boiler  efficiencies  of  from  75  to  80 
per  cent  were  obtained,  but  the  capacity  was  limited.  When 
sufficient  draft  was  applied  to  introduce  a  considerable 
amount  of  coal,  the  velocity  was  such  as  to  carry  unconsumed 
particles  of  coal  into  the  back  connection  and  tubes.  When 
fuel  was  introduced  into  the  powdered  fuel  furnace  at  a  rate 
which  gave  the  full  rated  capacity  of  the  boiler,  a  particle 


FIG.  51. — Schwartzkopf  Apparatus. 

remained  in  the  combustion  zone  of  an  ordinary  furnace 
less  than  half  a  second. 

In  1910,  Mr.  J.  E.  Blake  installed  under  a  300-horse- 
power  water-tube  boiler  at  the  Henry  Phipps  power  plant 
the  arrangement  shown  in  Fig.  52.  The  pulverizer  served 
as  its  own  blower,  sending  the  powdered  coal,  mixed  with 
air,  to  the  furnace;  where,  in  this  installation,  it  was  intro- 
duced by  a  series  of  nozzles  extending  across  the  width  of 
the  furnace.  A  little  less  than  the  rated  horse  power  of 
the  boiler  was  obtained,  with  an  efficiency  of  about  79  per 
cent. 

A  later  form  of  the  Blake  apparatus  was  installed  in  the 
winter  of  1913  at  the  Peter  Doelger  brewery  in  New  York. 
The  powdered  coal  was  delivered  into  the  top  of  an  exten- 


POWDERED  COAL  UNDER  BOILERS 


143 


144  POWDERED  COAL  AS  A  FUEL 

sion  furnace  or  "  Dutch  oven."  Smokeless  combustion  and 
high  efficiency  were  obtained,  the  principal  trouble  being 
from  slag,  which  accumulated  on  the  roof  and  side  of  the 
furnace  and  piled  up  in  such  masses  upon  the  floor  that  fre- 
quent shut-downs  were  required  for  its  removal.  As  much 
water  was  evaporated  with  1000  Ib.  of  the  powdered  coal 
as  had  formerly  been  evaporated  with  1400  Ib.  of  ordinary 
coal,  but  the  cost  of  furnace  maintenance,  the  frequent 
laying-off  of  the  boiler  for  the  removal  of  slag,  and  the  cost 
of  pulverizing,  counteracted  this  advantage  and  the  system 
was  abandoned  after  a  trial  of  about  eight  weeks. 

Mr.  Claude  Bettingdon  of  Johannesburg,  South  Africa 
(located  in  a  section  where  the  price  of  coal  is  high),  attacked 
the  problem  by  designing  a  boiler  especially  for  use  with 
powdered  coal.  He  took  out  his  first  patent  in  the  United 
States,  but  the  boiler  was  first  commercially  exploited  in 
England.  In  this  boiler,  the  feed  is  upward,  as  shown  in 
Fig.  53,  through  a  water-jacketed  nozzle  in  the  center  of  a 
vertical  furnace.  The  pulverizer  acts  as  a  blower,  and  the 
air  supply  is  preheated.  From  the  pulverizer  the  coal  passes 
to  a  separator,  where  the  larger  particles  settle  out  and  return 
again  to  be  treated,  the  finer  passing  on  as  coal  in  suspension. 
As  a  particle  has  to  pass  twice  the  length  of  the  furnace 
(upward  and  downward)  to  escape,  there  is  no  difficulty  in 
obtaining  complete  combustion. 

The  inner  row  of  tubes  of  the  circular  furnace  are  covered 
with  a  special  refractory  covering  to  within  a  short  distance 
of  the  bottom  header,  making  a  brick-lined  combustion 
chamber.  Special  bricks  are  placed  loosely  around  the 
tubes,  but  they  soon  become  coated  with  molten  ash  and 
slag,  which  weld  them  into  a  solid  wall  and  close  the  crevices 
between  the  lining  and  the  top  header.  The  ash  which  is 
not  so  slagged  to  the  furnace  surfaces,  or  carried  out  by  the 
draft,  drips  into  the  ash  pit  below  the  lower  header.  The 
destructive  effect  of  an  impinging  flame  upon  the  brick- 
work is  avoided  by  receiving  the  flame  upon  the  lower  head 
of  the  central  drum,  or  upon  the  accumulation  of  gas  in 


POWDERED  COAL  UNDER  BOILERS 


145 


v,  { 

Special  B rich 
.§»        Forming 
"^      Combustion 

Chamber. 

Horizontal  Section- 
A-B. 


^Superheater 

Flooding  and 
Blow-out  Pipes. 


FIG.  53. — Bettington  Boiler. 


146  POWDERED  COAL  AS  A  FUEL 

the  upper  end  of  the  chamber.  The  region  of  greatest  heat 
intensity  is  in  the  core,  while  the  tubes  and  shell  are  sub- 
jected to  the  lesser  temperatures  of  the  somewhat  cooled 
gases,  which  have  not  yet  passed  away.  The  radiant 
heat  is  very  effective  upon  tubes  and  shell,  and  the  metal 
surfaces  must  be  kept  perfectly  clean.  Particular  care  must 
be  taken  as  to  the  water  level.  One  of  these  boilers  having 
2606  sq.ft.  of  heating  surface  has  been  running  for  over 
four  years  at  the  works  of  the  builders.  It  evaporates 
regularly  14,000  Ib.  and  has  been  worked  up  to  22,000  Ib. 
of  water  per  hour.  These  rates,  however  (5.4  and  8.4  Ib. 
per  square  foot  of  heating  surface)  are  attained  with  stoker- 
fired  boilers  using  ordinary  coal. 

A  contributor  to  Power  who  has  had  two  of  these  boilers 
in  charge  says  that  the  steel  head  of  the  upper  drum  burned 
through  at  one  time,  probably  because  dirt  collected  upon 
it;  and  that  in  spite  of  the  cooling  effect  of  the  tubes  the 
special  bricks  forming  the  furnace  quickly  burn  away, 
and  frequent  renewals  are  necessary.  Care  must  be  taken 
lest  the  lining  burn  through  and  the  gas  be  short-circuited. 
Although  this  boiler  will  burn  low-grade  coals  successfully, 
and  while  under  steam  is  easily  managed,  one  fireman  being 
able  to  look  after  several  boilers,  these  advantages  are  largely 
offset,  in  his  opinion,  by  high  cleaning  and  maintenance 
charges. 

The  makers  say  their  experience  has  been  that  a  lining 
will  last  about  two  years,  and  that  even  large  holes  will 
automatically  seal  up.  The  parts  which  require  most  fre- 
quent renewals  are  the  beaters  and  liners  of  the  pulverizer. 
These  are  of  manganese  steel,  and  can  be  replaced  in  about 
two  hours.  The  makers  claim  an  approximate  life  for  the 
beaters  corresponding  with  1500,  and  for  the  liners  with 
2000  tons  of  coal  handled.  A  user,  after  ten  months  of 
experience,  says  that  the  set  of  blades  runs  from  1000  to 
1200  hours.  The  use  of  heated  air  in  the  pulverizer  allows 
coal  having  15  per  cent  or  more  of  moisture  to  be  handled 
successfully;  a  separate  heater  or  dryer  is  recommended  with 


POWDERED  COAL  UNDER  BOILERS 


147 


large  boilers.  The  makers  allow  2  to  3  per  cent  of  the  boiler 
capacity  for  pulverizing.  There  has  been  some  trouble  from 
leaky  water  jackets,  putting  the  flame  out,  but  this  has 
been  overcome  by  the  use  of  welded  jackets.  The  CO2 
is  carried  at  about  15  per  cent  in  regular  practice.  The 
possibility  of  getting  an  adequate  supply  of  oxygen  to  the 
finely  comminuted  carbon  facilitates  perfect  and  smokeless 
combustion  with  a  minimum  air  supply,  but  with  the  rates 
of  combustion  demanded  in  present  practice  the  result 
is  often  an  excessively  high  temperature  with  erosive  and 
reducing  characteristics  which,  however  good  they  may  be 
for  metallurgical  purposes,  are  not  favorable  to  the  longevity 
of  a  boiler  furnace.  If  this  temperature  is  kept  down  by 
feeding  less  fuel,  the  capacity  is  limited,  while  if  it  is  kept 
down  by  using  an  excess  of  air  the  economic  advantage  just 
cited  is  sacrificed. 

Boiler   at   Works  of  the   General   Electric  Company.     Mr. 
A.  S.  Mann  has  described  in  the  General  Electric  Review 


This  pipe  can  be  any  length 

(lOOftor  more)  Mag  be  run    .,nri .. ._/ -._  fjl 
underground  or  overhead.     Vacuum  *»« 


FIG.  54. — B.  &  W.  Boiler  for  Powdered  Coal. — General  Electric  Company. 

some  interesting  results  from  the  burning  of  powdered  coal 
under  a  boiler.     He  fitted  up  an  old  boiler  furnace  to  burn 


148  POWDERED  COAL  AS  A  FUEL 

coal  dust.  It  was  a  single  474  horse-power  (10  sq.ft. 
rating)  unit  that  had  formerly  been  fitted  with  an  extension 
front,  making  a  4-ft.  Dutch  oven,  for  burning  oil.  He  used 
the  same  oven  and  the  same  front  for  the  coal  furnace,  but 


FIG.  55.— Powdered  Coal  in  B.  &  W.  Boiler. 

the  internal  arrangements  were  altered.  Fig.  54  shows  a 
longitudinal  section  of  this  furnace,  Fig.  55  is  a  photograph 
of  the  front,  and  Fig.  56  is  a  diagram  of  the  front. 

The  same  feeders  and  the  same  driving  gear  are  used  as 
those  shown  in  Figs.  34  and  40.     In  order  to  perfect  the 


POWDERED   COAL  UNDER  BOILERS 


149 


mixture  and  to  supply  both  air  and  coal  in  small  quantities 
six  burners  and  six  feeders  were  used.  Air  is  admitted 
at  six  separate  ports;  that  is,  each  particle  of  coal  encounters 
six  air  currents  before  it  passes  on  to  the  heating  surface; 
and  every  air  current  is  pointed  across,  or  at  an  angle  with, 
the  burning  current,  thus  making  the  stirring  action  perfect. 
In  consequence,  combustion  is  virtually  complete  in  8  ft. 
of  travel  even  when  carrying  200  per  cent  of  normal  load. 
Five  hundred  and  twenty  pounds  per  front  foot  of  furnace 
have  been  burned  with  only  7  ft.  between  header  and  floor 
line.  The  boiler  has  carried  265  per  cent  load  long  enough 
to  show  that  such  loads  are  possible,  and  220  per  cent  or 


Rnzheatcr  in   !  :    •  j 
Arch- 


'S///Y 

y 


FIG.  56. — Front  of  Boiler. — General  Electric  Co. 

more  can  be  carried  indefinitely,  for  there  are  no  cleaning 
periods. 

The  six  burners  across  the  furnace  front  are  so  arranged 
that  the  air  currents  issuing  from  them  revolve  in  counter 
directions  with  respect  to  each  pair.  The  diagram  of 
Fig.  57  shows  this  relationship.  The  air  currents  act  like  a 
train  of  toothed  gears  at  the  tuyere  mouth  and  so  tend  to 
preserve  a  path  of  travel  normal  to  the  general  gas  current. 
These  swirling  masses  proceed  a  little  way  only,  when  they 
meet  with  air  from  the  arch  ports.  Fig.  58  shows  this 
movement.  The  swirls  move  onward  in  a  corkscrew  path, 
and  are  met  with  hot  air  from  A.  The  result  is  the  curve  D. 


150 


POWDERED  COAL  AS  A  FUEL 


The  whole  volume  follows  this  path  and  can  be  plainly 
seen  at  light  loads  making  its  turn  beneath  the  arch.  There 
are  six  curves  like  D,  one  for  each  burner,  and  each  curve 


FIG.  57. — Arrangement  of  Burners. — B.  &  W.  Boiler. 

is  a  corkscrew  at  least  part  way.     The  side  wall  currents  help 
to  prolong  the  mixing  action. 

One  difficulty  presents  itself  in  burning  powdered  coal 
that  is  not  met  in  burning  coal  by  the  usual  processes. 
Powdered  coal  is  burned  in  suspension,  and  as  it  travels  at 
40  or  50  ft.  per  second  it  must  be  consumed  in  one-sixth 


FIG.  58. — Air  Currents  in  Boiler  Furnace. 

second  or  so.  If  it  is  not,  it  will  not  be  completely  oxidized. 
During  this  brief  time  interval  there  is  only  one-fifth  of  a 
pound  burning  in  this  boiler,  even  at  heaviest  loads.  At  no 


POWDERED  COAL  UNDER  BOILERS 


151 


instant  is  there  a  greater  quantity  of  coal  than  this  in  the 
furnace.  With  a  grate,  no  coal  particle  need  burn  in  a  short 
time,  the  average  time  for  all  particles  being  half  an  hour, 
for  there  is  a  ton  and  a  half  or  so  on  the  grate,  burning 
slowly.  This  apparent  disability  really  works  to  the 
advantage  of  powdered  coal. 

For  starting  a  first  fire  beneath  this  boiler,  an  armful 
of  kindling  was  placed  at  the  mouth  of  one  burner  and 
lighted;  then  secondary  air  was  admitted  at  this  burner, 
followed  by  primary  air.  A  switch  started  a  motor  and  its 
feeder,  sending  down  coal;  and  with  a  puff  of  smoke  the 
fire  was  going.  The  next  burner  caught  from  the  first  and 
so  two  more,  making  four  in  all,  were  set  at  work.  The 
memorandum  taken  at  the  time  was: 

8:26  A.M.,  light  fire,  four  burners  f  on; 
8:33  A.M.,  10  Ib.  pressure; 
8:46  A.M.,  140  Ib.  pressure. 

At  8 :46  A.M.  the  fireman  checked  his  coal  feed  and  went  up 
overhead  to  open  the  stop  valve,  and  in  two  more  minutes 
the  boiler  was  carrying  its  load. 

This  fire  was  started  in  a  new  cold  furnace  beneath  a 
boiler  full  of  cold  water.  With  half  the  coal-burning  capacity 
in  use,  pressure  was  up  in  twenty  minutes. 

The  first  boiler  trial  gave  68  per  cent  efficiency  with 
131  per  cent  of  normal  load.  Efficiencies  were  calculated 
by  dividing  the  heat  in  the  steam  by  the  heat  in  the  coal 
(laboratory  test)  that  produced  it.  That  is,  if  there  were 
realized  10  Ib.  of  equivalent  evaporation  per  pound  of  coal 
and  the  coal  contained  14,000  B.t.u.,  the  efficiency  was 
(10  X  966)  ^  14,000  =  0.69.  Successive  trials  gave  the  results 
shown  in  the  table  below: 

RESULTS  OF  BOILER  TRIALS 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

Load,  per  cent  

131 

186 

212 

119 

97 

136 

154 

154 

141 

164 

205 

Efficiency,  per  cent  . 
Air,  cu.ft.  per  Ib.  coal 

68 
210 

63.8 

178 

65.8 
150 

68 
190 

71.8 
250 

65.5 
181 

71 

200 

69.4 
226 

66.1 
216 

63.7 
168 

75.7 
208 

Flue,  temperature.  . 

559 

684 

786 

583 

568 

652 

693 

685 

628 

678 

724 

152  POWDERED  COAL  AS  A  FUEL 

Since  the  last  and  best  trial  the  boiler  has  given  as  good 
or  better  efficiencies  for  a  week  at  a  time,  including  coal  for 
all  purposes,  and  using  railroad  weights  for  coal,  the  fire 
being  put  out  at  5  P.M.  and  kindled  fresh  at  7:30  A.M.  every 
day. 

The  earlier  experiments  showed  nothing  remarkable  in 
economy,  but  in  the  beginning  it  was  not  known  how  much 
air  to  use  or  where  best  to  admit  it.  After  experiment  No.  5, 
observations  began  to  coordinate.  Nos.  7  and  8  were  in- 
structive, but  some  mistakes  were  made  before  reaching 
No.  11,  and  this  was  not  final.  Better  work  can  be  done 
with  less  air,  though  perhaps  there  are  many  fires  not 
giving  75.7  per  cent  efficiency  at  205  per  cent  load. 

Mr.  Mann  experimented  in  a  comprehensive  way  with 
air  dampers,  noting  air  volumes,  flue  temperatures  and  color 
of  smoke.  Each  air  supply  had  its  damper,  and  these  were 
adjusted  independently.  With,  a  given  coal  feed  if  it  was 
found  that  changing  the  points  of  application  of  air  permitted 
a  reduction  in  air  volume,  with  an  accompanying  rise  in  flue 
temperature  and  with  no  smoke,  it  was  concluded  that  an 
improvement  was  being  made. 

In  this  way  it  was  found  best  to  admit  as  little  air  at 
A  and  B  as  possible,  a  great  deal  at  C,  some  at  D,  and  a  little 
at  E  (F  is  used  only  on  heaviest  loads,  that  is  above  210 
per  cent).  In  general  it  may  be  stated  that,  as  the  air 
supply  departs  from  200  cu.ft.  per  pound  of  coal,  efficiency 
falls. 

The  operator  is  supplied  with  gauges  which  gave  him 
the  heights  of  water  column  corresponding  with  definite 
air  volumes.  Each  gauge  is  marked  with  its  corresponding 
number  of  coal  notches  on  feeder  rheostats.  The  fireman 
thus  makes  the  water  column  fix  his  coal  feed.  Dampers 
axe  marked  and  results  are  definite. 

It  is  to  be  observed  that  in  measuring  air  the  volume 
is  much  better  than  measuring  the  CO2  in  chimney  gases. 
Two  hundred  feet  of  air  gives  CO2  of  about  15.3  per  cent; 
208  ft.  gives  14.7  per  cent;  and  this  small  change  (which 


POWDERED   COAL  UNDER   BOILERS  153 

no  C02  apparatus  can  be  sure  of)  gives  a  marked  change  in 
evaporation.  The  same  change  in  air  volume  makes  the 
water  column  move  J  in.  Furthermore,  the  fireman  knows 
of  any  change  instantly.  He  measures  it  and  he  measures 
all  of  the  air:  while  the  C02  content  is  judged  from  a 
minute  sample  and  is  half  an  hour  behind  the  time. 

It  will  pay  so  to  arrange  the  air  piping  on  any  boiler  that 
air  volumes  can  be  measured  instantly,  and  this  is  true 
whether  a  chimney  or  a  fan  produces  the  draft.  A  nozzle 
plug  is  used  in  the  pipe,  though  perhaps  a  Pitot  tube  might 
do;  however,  the  nozzle  plug  acts  well  and  it  is  liked. 
If  a  fireman  sees  his  water  column  go  up  he  knows  that  a 
hole  is  coming  in  his  fire  and  he  knows  it  right  away.  This 
knowledge  is  of  more  value  to  him  than  any  other  informa- 
tion of  the  sort  he  could  have. 

Boiler  trials  already  made  point  the  way  to  improvement. 
There  is  enough  heat  in  the  flue  gases  to  warrant  the  placing 
of  heating  surface  in  its  path.  Everything  in  the  shape  of 
tar  has  been  burned  out  of  the  fuel,  and  it  is  planned  to  put 
about  600  ft.  of  l|-in.  tubing  in  the  breeching  and  send 
feed  water  through  it.  The  stack  is  clear.  All  soot  drops 
in  the  gas  chambers  long  before  reaching  the  stack,  so  that 
all  troubles  commonly  met  with  on  this  account  are  absent. 
More  trials  will  be  conducted  when  this  addition  is  ready. 

Other  losses  are  not  great.  Radiation  from  the  furnace 
is  small,  for  the  furnace  is  virtually  surrounded  with  air 
passages,  and  heat  that  gets  into  them  is  returned  to  the 
furnace.  These  air  passages,  and  the  deflecting  ah-  currents, 
C,  D,  E,  and  F,  do  much  toward  protecting  the  furnace  walls. 
One  arch  has  been  burned  out.  It  melted  down  from  9  in. 
to  4  in.,  when  it  fell,  but  it  has  stood  up  nearly  six  months. 
It  did  not  run  every  day  with  heavy  load  and  did  not  run 
nights  at  all;  but  it  was  made  of  common  fire  bricks  which 
are  not  intended  for  high  temperatures.  The  new  arch  is  of 
better  material,  the  bricks  costing  $37.00  per  thousand. 
It  may  pay  to  use  carborundum. 

As  to  how  much  it  costs  to  fire  boilers  with  powdered  coal, 


154  POWDERED   COAL  AS  A  FUEL 

that  depends  upon  how  much  is  made.  Coal  has  to  be 
crushed,  elevated,  dried  and  distributed,  whatever  burning 
system  is  used.  There  are  two  elevations  and  the  additional 
pulverizing  for  powdered  coal.  The  question  of  real  interest 
is,  how  much  more  does  it  cost  to  prepare  and  burn  coal  than 
by  the  usual  process.  In  this  plant,  the  pulverizer  is  small, 
and  the  first  cost  with  motor  installed  was  about  $1000 
per  ton  pulverized  per  day.  If  it  were  to  run  only  five  hours 
a  day,  leaving  ample  time  for  repairs,  fixed  charges  would 
amount  to  about  7  cents  per  ton,  allowing  10  per  cent  per 
year. 

Electric  current  costs,  in  cents  per  ton,  are  as  follows: 
Driving  dryer,  1.95;  two  elevations,  0.77;  pulverizing,  14.8; 
which  makes  17.52  cents  per  short  ton  for  current  and 
24.52  cents  total  cost  including  fixed  charges.  This  total 
is  reduced  by  about  one-third  with  large  pulverizers. 

The  pulverizer  calls  for  some  attention,  but  it  is  in  the 
coal  house  with  other  machinery  and  whatever  labor  it 
needs  is  more  than  made  up  in  decreased  labor  of  firing.  The 
blower  at  the  furnace  gives  a  pressure  of  3  oz.,  which  is 
ample.,  so  that  25  cents  additional  per  ton  is  all  that  can  be 
charged  against  pulverized  coal.  The  plant  has  not  run 
long  enough  to  say  what  the  cost  of  repairs  will  be,  but  two 
years  of  experience  have  shown  that  it  is  nominal,  or  at 
least  no  greater  than  is  met  with  in  all  coal-handling  ma- 
chinery. 

Figs.  59  and  60  show  the  plan  of  a  powdered  coal  plant 
which  the  Fuller  Engineering  Company  have  recently 
installed  for  the  Missouri,  Kansas  &  Texas  Railroad,  at 
Parsons,  Kansas.  This  plant  will,  when  completed,  contain 
ten  250  horse-power  Heine  boilers;  although  at  the  present 
time  only  eight  boilers  are  installed. 

Fig.  61  gives  a  cross-section  through  the  boiler  setting 
and  shows  just  how  the  powdered  coal  is  handled  into  the 
combustion  chambers. 

The  engineers  of  this  plant  made  the  following  replies 
to  questions  submitted  by  the  author: 


POWDERED  COAL  UNDER  BOILERS 


155 


156 


POWDERED  COAL  AS  A  FUEL 


POWDERED   COAL  UNDER  BOILERS 


157 


158  POWDERED   COAL  AS  A  FUEL 

1.  The  amount  of  coal  burned  per  horse  power  depends 
strictly  upon  the  quality  of  coal  burned.     It  is  safe  to  assume 
that  a  boiler  efficiency  of  not  less  than  75  per  cent  can 
readily   be   obtained  with  powdered   coal   as   a  fuel.     In 
our  practice  we  base  our  calculations  on  using  1293  heat 
units  per  pound  of  water  from  and  at  212°.     The  equivalent 
evaporation  obtained  per  pound  of  coal  burned  should  equal 
the  heat  value  of  the  coal  used  divided  by  1293. 

2.  The  steam  pressure  will  be  150  lb.,  and  with  feed 
water  at  a  temperature  of  200°  the  factor  of  evaporation  will 
be  1.0584. 

3.  As  to  feed  control,  there  will  be  located  directly  below, 
and  attached  to,  the  powdered  coal  storage  bin,  a  feed-screw 
operating  inside  of  a  bored  cast  pipe  with  very  little   clear- 
ance (to  prevent  the  coal  from  rushing  around  the  screw 
or  passing  the  screw  when  in  operation).     The  feed-screw  is 
driven  by  means  of  a  motor,  driving  directly  to  a  speed 
regulator,  and  then  through  the  speed  regulator  to  the  feed 
screw.     Air  supply  for  carrying  the  coal  into  the  furnace 
and  for  combustion  will  be  furnished  by  a  fan  driven  by  a 
direct-connected  motor.     There  will  be  one  fan  for  each 
two  boilers.     There  are  gates  located  in  each  blast  pipe 
leading  to  the  combustion  chambers,  and  also  a  regulating 
cone  for  varying  the  effective  area  between  the  blast  pipe 
and  the  outside  pipe,  at  the  entrance  point  in  the  front  wall 
of  combustion  chamber.     The  regulating  cone  controls  the 
percentage  of  excess  air  induced.     By  means  of  the  equip- 
ment outlined,  positive  control  of  the  amount  of  coal  as  well 
as  of  the  amount  of  air  supplied  will  be  attained  and  also  the 
pressure  of  air  admitted  to  the  furnace  will  be  under  control. 

4.  The  fireman  will  be  governed  in  making  adjustments 
by  conditions  and  by  the  demand  for  steam.     With  proper 
apparatus  at  hand,  he  will  be  able  to  regulate  the  supply 
at  all  times.     Firemen  having  had  some  experience  with 
powdered  coal  burning  should  be  able  to  judge  by  the  appear- 
ance of  the  furnace  whether  proper  combustion  is  being 
obtained. 


POWDERED  COAL  UNDER  BOILERS  159 

5.  With  the  furnace  properly  designed  and  proportioned 
to  the  quantity  of  tcoal  to  be  burned,  no  serious  effects  will 
occur  because  of  flame  impingement  against  the  bridge  wall. 
Furnaces  for  burning  powdered  coal  are  to-day  designed 
so  that  excessive  velocities  are  eliminated.     High  velocities 
cause  destructive  conditions. 

6.  It  is  not  expected  that  the  conveyor  screw  will  break 
with  properly  designed  feeding  mechanism,  but  an  extra 
screw  should  be  on  hand.     Slides  are  located  between  the 
feeder  and  the  bin  proper,  so  that  should  any  accident  occur 
requiring  the  insertion  of  a  new  feed-screw,  this  can  readily 
be  done.     The  bin  capacity  is  designed  to  suit  operating 
conditions.     A  ten-hours7  supply  can  easily  be  stored  in 
bins  in  front  of  the  boilers,  and  more  if  desired.     The  design 
of  the  bins,  however,  should  be  such  that  when  coal  is  being 
fed  from  the  bottom  the  majority  of  the  coal  is  in  motion. 

7.  With   coal   properly   prepared   and   pulverized   and 
burned  in  a  properly  designed  furnace,  75  to  80  per  cent 
of  the  ash  will  deposit  in  the  combustion  chamber,  the 
balance  of  the  ash  being  so  fine  after  the  carbon  is  burned 
out  that  it  is  carried  away  as  a  light  haze. 

8.  The  coal  will  not  cake  in  the  bin  in  a  properly  managed 
plant,  or  in  one  which  has  suitable  equipment.     The  drying 
apparatus  is  sufficiently  large  to  take  care  of  the  maximum 
powdered  coal  demand. 

9.  There  are  38  Ib.  of  powdered  coal  to  a  cubic  foot. 

10.  So  far  as  we  know  the  boilers  will  be  intermittently 
fired,  operating  full  during  the  day  and  at  about  one-quarter 
capacity  at  night. 

11.  We  have  raised  steam  in  a  400-horse-power  Rust 
boiler  with  cold  setting,  and  with  feed  water  at  180°,  in 
forty-five  to  fifty-five  minutes,  to  150  Ib.  gauge  pressure. 
However,  this  practice  is  not  good  as  it  forces  the  setting 
somewhat  and  is  likely  to  cause  trouble  with  the  furnace 
walls. 

A  successful  installation  for  burning  powdered  coal  under 
a  boiler  has  been  in  continual  service  since  March,  1915,  at 


160  POWDERED  COAL  AS  A  FUEL 

the  works  of  the  American  Locomotive  Co.,  Schenectady, 
N.  Y.  Some  data  on  this  plant  are  given  by  Mr.  C.  L. 
Heisler  in  the  Journal  of  the  A.S.M.E.  for  December,  1916. 
The  percentage  of  CCb,  by  a  recording  chart  checked  by  the 
Orsat  apparatus,  is  rarely  under  16  and  is  oftener  above  17. 
The  boiler  is  one  of  a  battery  of  Franklin  water-tube  boilers, 
the  rest  of  which  employ  mechanical  stokers.  It  was  fitted 
with  a  deep  hopper-shaped  furnace  extending  the  whole 
length  of  the  boiler  and  tapering  down  to  a  slag  pit  at  the 
bottom,  without  vertical  walls  or  arches.  The  coal  enters 
the  front  end  at  an  angle  of  about  45°  with  the  vertical. 
The  9-in.  front  sloping  furnace  wall  is  supported  by  a  row 
of  scrap  boiler  tubes.  The  lower  row  of  water  tubes  is 
shielded  at  the  rear  half  of  its  length  by  the  ordinary  tiling 
of  a  Heine  setting. 

Coal  is  fed  by  a  screw  feeder  from  a  hopper  into  the  air 
blast  at  a  point  about  3  ft.  away  from  the  furnace  tuyeres. 
Three  tuyeres  are  used,  consisting  of  wrought-iron  pipe 
nipples,  10  by  24  in.  The  air  blast  pressure  is  from  J  to 
1J  oz.,  atmospheric  pressure  is  maintained  in  the  furnace, 
and  there  is  a  slight  suction  inward  at  the  slag  hole  at  the 
base  of  the  furnace. 

The  sloping  side  walls  of  the  furnace  are  coated  with  1  to 
3  in.  of  slag  and  are  in  perfect  condition.  No  trouble  is 
experienced  from  coke  or  cinders  clogging  the  spaces  between 
the  water  tubes.  Repairs  have  been  trifling.  Evapora- 
tive tests  have  shown  a  materially  higher  efficiency  than 
could  be  obtained  from  a  duplicate  boiler  with  ordinary 
coal  fired  by  mechanical  stokers,  and  a  much  quicker  re- 
sponse is  made  to  sudden  demands  for  steam.  An  ordinary 
fireroom  helper  was  able  to  give  the  furnace  all  the  attention 
required. 


CHAPTER  IX 
POWDERED   COAL  FOR  LOCOMOTIVES 

MR.  J.  E.  MUHLFELD,  in  a  paper  read  before  the  New 
York  Railroad  Club  at  its  February,  1916,  meeting,  and  in  a 
subsequent  paper  presented  to  the  A.S-M.E.  at  its  meeting 
of  December,  1916,  has  presented  data  on  the  application 
of  powdered  coal  to  locomotives  from  which  the  following 
is  largely  abstracted. 

The  present  annual  consumption  of  powdered  coal  in  the 
United  States  is  over  8,000,000  tons.  The  general  use  of  this 
fuel  in  industrial  kilns  and  furnaces  has  demonstrated  its 
effectiveness  and  economy". 

The  expenditure  for  locomotive  fuel  (which  the  Inter- 
state Commerce  Commission  reports  as  $249,507,624,  or 
about  23  per  cent  of  the  transportation  expenses  of  242,657 
operated  miles  of  steam  railway  in  the  United  States,  for  the 
fiscal  year  ending  June  30,  1915)  is,  next  to  labor,  the  largest 
single  item  of  cost  in  steam  railway  operation. 

The  necessity  for  conserving  the  limited  supply  of  oil 
in  the  rapidly  exhausting  fields  for  other  than  locomotive 
purposes  will  shortly  eliminate  it  from  railway  motive  power 
use. 

The  large  quantity  of  steam  used  by  the  modern  loco- 
motive necessitates  high  rates  of  evaporation,  and  these 
can  be  economically  obtained  only  by  some  means  for  burn- 
ing solid  fuel  other  than  on  grates;  in  order  to  reduce  the 
waste  due  to  the  loss  of  combustible  dust  and  that  from 
imperfect  combustion. 

Steam  locomotives  must  be  equipped  to  approximate 
more  nearly  the  electric  locomotive,  with  regard  to  the 
elimination  of  smoke,  soot,  cinders  and  sparks;  the  reduction 
of  noise,  time  for  dispatching  at  terminals,  and  stand-by 

161 


162  POWDERED   COAL  AS  A  FUEL 

losses;  and  the  increasing  of  the  daily  mileage  by  longer 
runs  and  more  nearly  continuous  service  between  general 
repair  periods. 

Workmen  of  a  higher  average  quality  should  be  induced 
to  enter  the  service  as  firemen,  eligible  for  promotion  as 
engineers,  by  reducing  the  arduous  work  now  required  to 
shovel  ahead  and  supply  coarse  coal  to  grates,  and  to  rake 
and  clean  fires  and  ash-pans. 

The  future  steam  locomotive  will  be  required  to  produce 
maximum  hauling  capacity  per  unit  of  total  weight,  at  the 
minimum  cost  per  pound  of  draw-bar  pull,  and  with  the 
least  liability  to  delay  because  of  mechanical  failures. 

In  meeting  the  conditions  outlined  above,  powdered 
coal  has  succeeded  because  of  the  following  advantages: 

1.  It  offers  opportunity  for  even  greater  accomplish- 
ments in  the  steam  railway  field  than  have  heretofore  been 
obtained  through  its  use  in  cement  kilns  and  in  metallurgical 
furnaces. 

2.  It  produces  a  saving  of  from  15  to  25  per  cent  in  coal 
of  equivalent  heat  value,  as  compared  with  hand  firing  of 
coarse  coal  on  grates.    Powdered  coal  may  run  as  high 
as  10  per  cent  in  sulphur  and  35  per  cent  in  ash  and  still 
produce  maximum  steam-heating  capacity;  so  that  other- 
wise unsuitable  and  unsalable  or  refuse  grades  of  coal  may 
be  utilized,  and  hence  the  saving  in  cost  per  unit  of  heat 
evolved  will  be  a  considerable  item. 

3.  It  enables  us  to  maintain  fire-box  temperatures  and 
sustained   boiler   capacities   equivalent   to   and    exceeding 
those  obtainable  from  crude  or  fuel  oil. 

4.  It  maintains  the  steam  locomotive  on  its  present 
relatively  low  first  cost  and  expense-for-fixed-charge  basis, 
and  further  reduces  the  cost  for  maintenance  and  operation 
of  large  units. 

5.  It  eliminates  the  waste  products  of  combustion  and 
fire  hazards,  and  permits  the  enlargement  of  exhaust  steam 
passages  and  thus  produces  increased  efficiency  at  the  cylin- 
ders. 


POWDERED  COAL  FOR  LOCOMOTIVES  163 

Commencing  with  Richard  Trevithick's  locomotive, 
which  was  built  in  1803,  and  was  the  first  actually  to  per- 
form transportation  service,  general  practice  has  been  to 
burn  wood,  coal  and  other  solid  fuels. in  locomotive  fire- 
boxes, on  grates. 

During  the  early  development  stages  this  method  pro- 
vided adequate  means  for  utilizing  the  relatively  high  grade 
available  fuel  effectively  and  economically,  as  the  rate  of 
combustion  per  square  foot  of  grate  surface  per  hour  were 
relatively  low.  But,  during  the  past  twenty-five  years, 
continued  increases  in  locomotive  tractive  force  have  so 
increased  required  rates  of  combustion  that  the  quantity  of 
fuel  used  per  unit  of  work  performed  is  far  beyond  what  may 
be  realized  by  more  effective  means  now  available. 

While  great  progress  has  been  made  in  the  superheating 
and  use  of  steam,  the  principal  improvements  that  have  been 
perfected  in  steam  generation  have  been  through  enlarged 
heating  surfaces  better  circulation  of  water,  regulation  of 
air  admission  and  the  use  of  fire-brick  arches. 

Early  Use  of  Powdered  Coal.  The  Manhattan  Railroad 
in  New  York  City  conducted  experiments  with  the  use  of 
coal  dust  in  one  of  their  locomotives  about  fifteen  years  ago. 
The  pulverizing  of  the  fuel  and  the  discharge  of  the  coal  and 
air  into  the  fire-box  were  accomplished  through  the  use  of  a 
combined  pulverizer,  blower  and  steam  turbine  located  on  the 
locomotive.  In  this  case  the  cylinder  exhaust  was  not 
used  to  produce  boiler  draft;  the  coal  dust  was  relatively 
coarse;  and  no  provision  was  made  for  precipitating  and 
cooling  the  furnace  slag;  all  of  which  factors  no  doubt  con- 
tributed to  the  failure  of  the  experiment. 

The  Swedish  Government  Railways  have  also  done  some 
experimental  work  in  the  burning  of  peat  and  coal  powder 
in  small  steam  locomotives  during  the  past  few  years,  the 
fuel  being  prepared  before  supplying  it  to  the  locomotive 
tender.  In  this  case  the  powder  was  blown  into  the  furnace 
by  steam  and  the  fire-box  brick  work  was  very  complicated. 

Various  other  experimental  efforts  have  been  made  by 


164  POWDERED  COAL  AS  A  FUEL 

railways  in  the  United  States  and  elsewhere,  but,  so  far  as  is 
known,  they  have  not  until  recently  resulted  in  regular  train 
operation. 

The  first  steam  railway  locomotive  of  any  considerable 
size  to  be  fitted  up  in  the  United  States  or  Canada  (or, 
so  far  as  is  known,  in  the  world)  with  a  successful  self- 
contained  equipment  for  the  burning  of  powdered  coal  in 
suspension  was  a  ten-wheel  type  engine  on  the  New  York 
Central  Railroad.  This  locomotive  has  22  by  26-in. 
cylinders;  69-in.  diameter  drivers;  200-lb.  boiler  pressure; 
55  sq.ft.  of  grate  surface;  is  equipped  with  Schmidt  super- 
heater and  a  Walschaerts  valve  gear;  has  31,000  Ib.  trac- 
tive power  and  was  first  converted  into  a  powdered  coal 
burner  in  the  early  part  of  1914. 

Since  the  development  of  that  application  similar  instal- 
lations have  been  made  on  a  Chicago  &  Northwestern 
Railway  Atlantic  type  locomotive,  and  also  on  a  new 
consolidation  type  of  locomotive  recently  built  for  the 
Delaware  &  Hudson  Company.  This  latter  locomotive 
is  probably  the  largest  of  its  type  in  the  world.  It  has 
63-in.  diameter  drivers  and  about  63,000  Ib.  of  tractive 
force,  having  been  designed  for  combination  fast  and 
tonnage  freight  service. 

This  latest  effort  toward  the  burning  of  powdered  coal 
in  steam  locomotives  has  now  passed  the  experimental 
stage,  and  arrangements  have  been  made  for  proceeding 
with  commercial  applications  as  rapidly  as  the  equipment 
can  be  produced. 

Any  solid  fuel  which  in  a  dry,  pulverized  form  will  have 
two-thirds  of  its  contents  combustible,  is  suitable  for  steam- 
generating  purposes. 

The  generally  recognized  waste,  unsalable  and  other- 
wise low-value  coal  mine  and  strip-pit  products,  such  as 
dust,  sweepings,  culm,  slack  and  screenings,  as  well  as 
lignite  and  peat,  are  suitable  as  are  the  larger  sizes  and  better 
grades,  for  drying  and  pulverizing  with  a  view  to  use  for 
steam-generating  purposes. 


POWDERED  COAL  FOR  LOCOMOTIVES 


165 


Reference  to  Figs. 
62  and  63  will  convey 
a  general  idea  of  the 
equipment  found 
essential  for  the  burn- 
ing of  powdered  coal 
in  a  steam  locomotive. 
The  particular  factors 
that  have  been  kept  in 
mind  in  the  develop- 
ment of  this  apparatus 
have  been: 

1.  To   produce 
equipment    that    will 
be   readily   applicable 
to  either  new  or  exist- 
ing steam  locomotives 
of  standard  design. 

2.  To  simplify  and 
standardize   the   vari- 
ous details  and  make 
them    interchangeable 
for  the  different  types 
and  sizes   of   locomo- 
tives. 

3.  To  apply  all  pos- 
sible operating  equip- 
ment,  in  a   self   con- 
tained manner,  to  the 
tender  fuel  tank;  elim- 
inating   complicated 
mechanism    for     con- 
veying fuel  from    the 
tender  to  the  engine, 
and  removing  from  the 
cab  all  special  appara- 
tus except  fuel  and  air 
supply  control  levers. 


166 


POWDERED  COAL  AS  A  FUEL 


4.  To  eliminate  the  necessity  for  any  manual  handling 
of  fuel,  fire  or  ashes  in  the  operation. 

5.  To  insure  positive  control  over  the  fuel  feed,  in  order 


to  meet  quickly  all  conditions  of  road  or  terminal  operation, 
and  to  provide  for  quick  firing-up,  free  steaming,  good 
combustion,  regularity  of  boiler  pressure,  uniform  fire-box 


POWDERED  COAL  FOR  LOCOMOTIVES  167 

temperature,  and  maximum  capacity  of  boiler,  with  the  mini- 
mum heat  loss. 

6.  To  place  the  entire  regulation  of  combustion  under 
three  hand-control  levers  in  the  cab;    i.e.,  fuel  feed,  air 
supply,  and  induced  draft  (the  last  employed  when  the  loco- 
motive is  not  using  steam). 

7.  To  provide  a  type  of  refractory  furnace  that  will  insure 
ready  accessibility  to  all  parts  of  the  fire  box  for  inspection 
and  maintenance. 

8.  To  insure  a  supply  of  dry  fuel  under  all  conditions 
of  weather. 

9.  To  eliminate  the  necessity  for  firing  tools,  such  as 
scoops,  rakes,  hoes,  slash-bars  and  grate  shakers,  as  well  as 
to  obviate  the  glare,  heat  effect,  and  lowering  of  fire-box 
temperature  and  draft  from  the  opening  of  the  furnace  door. 

10.  To  minimize  the  noise  and  dust  in  the  cab. 

11.  To    reduce    necessary    engine-house    facilities    and 
delays,  and  expenses  incident  to  building,  preparing,  clean- 
ing and  dumping  fires  and  hostlering  locomotives. 

12.  To  make  the  powdered  coal  burning  and  storage 
equipment  on  the  engine  and  tender  readily  convertible  for 
the  use  of  fuel  oil. 

In  the  application  of  powdered  coal  burning  equipment 
to  existing  types  of  steam  locomotives,  the  following  con- 
stitute all  the  changes  that  are  necessary: 

Smoke  Box.  Remove  the  existing  diaphragm,  table  and 
deflector  plates,  nettings,  hand  holes  and  cinder  hoppers, 
enlarge  the  exhaust  nozzle  opening. 

Fire  Box.  Remove  the  existing  grates,  ash  pans,  fire 
doors  and  operating  gear;  utilize  the  usual  arch  tubes  and 
sectional  type  of  brick  arch;  and  install  fire-brick-lined 
fire  pan,  primary  arch,  fuel  and  air  mixers  and  nozzle. 

Cab.  Install  regulating  levers  for  furnace  door,  fuel 
and  air  supply. 

Tender.  Install  enclosed  fuel  container  equipment  with 
fuel  and  pressure  air  conveying,  feeding,  commingling  and 
discharge  apparatus,  and  steam  turbine  or  motor  mechanism. 


168 


POWDERED   COAL  AS  A  FUEL 


Boiler 


FIG.  64— Single-unit  Gravity  Milling  Plant,  Hudson  Coal  Co.     Capacity 

2  Tons  per  Hour 


POWDERED  COAL  FOR  LOCOMOTIVES 


169 


Engine  and  Tender  Connections.  These  are  made  by 
the  use  of  one  or  more  sections  of  hose,  which  connect  the 
fuel  and  pressure  air  outlets  on  the  tender,  with  the  fuel 
and  pressure  air  nozzles  on  the  engine.  Metallic  flexible 


; 

future 

1  — 

~/"\>  — 
•*•  --tj  *s' 

Bin     x 

Future 
<S  Pulverizer  _^ 

()               "  ~  ffe$?A 

Kg 

!  i  Future  Dryer  .     JB 

OSI 

L 

3 

>c 

Motor 

0                           13 

-.--% 

>r 

CLLpcomotive  
Coaling  Tra 

r~X 

Collector 


Crushed  Coal 
bin ,10  Ton  Cap'y. 

'-•Feeder 

DriedCoats 
tor' 


Dried  Coal  Bin 
-'10  Tons  Copy. 


FIG.  65. — Double-unit  Plant  and  Single-bin  Locomotive  Coaling  Station. 
Capacity  8  Tons  per  Hour. 

conduits  are  employed  for  conveying  the  fan  blast  and  fuel- 
feeding  motive  power. 

Operation.  For  firing  up  a  locomotive,  the  usual  steam 
blower  is  turned  on  in  the  stack,  a  piece  of  lighted  waste 
is  then  passed  through  the  fire-box  door  opening  and  placed 
on  the  furnace  floor,  just  ahead  of  the  primary  arch,  after 
which  the  pressure  fan  and  one  each  of  the  fuel  and  pressure 
air  feeders  are  started. 


170 


POWDERED  COAL  AS  A  FUEL 


POWDERED  COAL  FOR  LOCOMOTIVES 

i— T- e7 


171 


172  POWDERED  COAL  AS  A  FUEL 

From  forty-five  to  sixty  minutes  is  ordinarily  sufficient 
to  get  up  200  Ib.  of  steam  pressure  from  boiler  water  at 
40°  F. 

After  firing  up,  the  regulation  of  the  fuel  and  air  supply 
is  adjusted  to  suit  the  standing,  drifting  or  working  condi- 
tions, the  stack  blower  being  used  only  when  the  locomotive 
is  not  using  steam. 

The  process  of  feeding  and  burning  powdered  coal  may  be 
briefly  stated  as  follows:  the  prepared  fuel,  having  been 
supplied  to  the  enclosed  fuel  tank,  gravitates  to  the  conveyor 
screws,  which  carry  it  to  the  fuel  and  pressure  air  feeders, 
where  it  is  thoroughly  commingled  with  and  carried  by  the 
pressure  air  through  the  connecting  hose  to  the  fuel  and 
pressure  air  nozzles  and  blown  into  the  fuel  and  air  mixers. 

Additional  air  is  supplied  in  the  fuel  and  air  mixers; 
and  this  mixture,  now  in  combustible  form,  is  drawn  into  the 
furnace  by  the  smoke-box  draft. 

The  flame  produced  when  the  combustible  mixture  enters 
the  furnace  obtains  its  average  maximum  temperature 
(from  2500  to  2900°  F.)  at  the  forward  combustion  zone 
under  the  main  arch;  and  at  this  point  auxiliary  air,  induced 
by  the  smoke-box  draft,  finally  completes  the  combustion 
process. 

The  smoke-box  gas  analysis  will  show  between  13  and 
14  per  cent  of  CO2,  when  coal  is  fired  at  the  rate  of  3000  Ib. 
per  hour;  between  14  and  15  per  cent  at  the  rate  of  3500  Ib. 
per  hour;  and  between  15  and  16  per  cent  at  the  rate  of 
4000  Ib.  per  hour;  so  that  as  the  rate  of  combustion  increases, 
there  is  no  falling  off  in  the  efficiency  of  combustion,  as  when 
coarse  coal  is  fired  on  the  grates. 

The  waste  of  fuel  from  the  stack,  where  ordinary  coal 
having  a  large  percentage  of  dust  and  slack  is  used;  the 
lowering  of  the  fire-box  temperatures  and  draft  by  the  open- 
ing of  the  fire  door;  and  the  resultant  variations  in  standing 
and  general  results  under  high  rates  of  combustion,  are 
entirely  eliminated  with  powdered  coal. 

The  uniformity  with  which  locomotives  can  be  firecl 


POWDERED  COAL  FOR  LOCOMOTIVES  173 

is  indicated  by  the  fact  that  regularly  assigned  firemen  can 
maintain  steam  within  two  pounds  of  the  maximum  allow- 
able pressure,  without  popping  off. 

As  each  of  the  fuel  and  pressure  air  feeders  has  a  range 
in  capacity  from  500  up  to  4000  Ib.  of  powdered  coal  per 
hour,  and  as  from  one  to  five  of  these  may  be  easily  applied 
to  the  ordinary  locomotive  tender,  there  is  no  difficulty  in 
meeting  any  desired  boiler  and  superheater  capacity. 

As  in  the  case  of  electric  locomotives,  but  little  actual 
operating  data  are  as  yet  available. 

The  first  complete  installations  of  a  fuel-drying  and  pul- 
verizing plant  and  locomotive  coaling  station,  in  combina- 
tion with  locomotives  equipped  for  burning  powdered  coal, 
will  be  made  by  the  Delaware  &  Hudson  Company  and  the 
Missouri,  Kansas  &  Texas  Railway,  and  these  are  not  yet 
ready  for  operation.  The  locomotives  so  far  equipped  on 
other  railways  are  still  depending  upon  the  outside  or 
inadequately  equipped  sources  for  then:  supply  of  powdered 
coal,  which  makes  the  handling  somewhat  difficult. 

Mr.  Muhlfeld  gives  the  following  record  from  tests  of  an 
Atlantic  type  passenger  locomotive,  fired  with  Kentucky 
unwashed  screenings,  83  per  cent  of  which  ran  100-mesh 
or  finer: 

LOCOMOTIVE  PERFORMANCE 

Miles  run 171 

Running  time,  hours 3 .87 

Train,  number  of  cars 5.8 

Train,  tonnage 291 

Speed,  miles  per  hour 44 . 2 

Drawbar  pull,  pounds 2711 

Horse  power 319 .5 

Fuel  used,  tons 3 .82 

Water  used,  gallons 8381 

Fuel  per  horse-power-hour,  pounds 6.17 

Water  per  horse-power-hour,  pounds 56 . 48 

Evaporation,  water  per  pound  of  coal,  pounds. ...  9.15 

Evaporation  from  and  at  212°  F.,  pounds 11.1 

Boiler  efficiency,  per  cent 77 


174 


POWDERED  COAL  AS  A  FUEL 


POWDERED  COAL  FOR  LOCOMOTIVES 


175 


Samples  of  gas  taken  from  the  smoke  box  gave  the  results 
below : 


Pounds  of  Coal 
Burned  per  Hr. 

Per  Cent  of 

CO2 

CO 

0 

3067 

14.5 

0.0 

4.5 

3498 

15.2 

0.0 

2.8 

3931 

15.2 

0.0 

4.0 

4000 

16.4 

0.4 

2.6 

On  a  10- wheel  locomotive  in  freight  service,  three  trials 
gave  the  results  subjoined: 


Item. 

PULVERIZED 

1 
Bitumin- 
ous. 

2 
Bitumin- 
ous. 

3 

Bitumin- 
ous. 

Fineness   per  cent  through  200-mesh  

0.85 
0.40 
24.72 
68.43 
6.85 
1.96 
14,739 
1,324 
61 
1,719 
26 
198.3 
7.15 
3.50 
562 
3,275 
12.84 

0.85 
0.81 
36.27 
58.29 
5.44 
0.68 
14,334 
426 
65 
1,808 
25 
193.5 
7.79 
3.22 
573 
3,063 
13.97 

0.85 
0.59 
24.36 
65.05 
10.59 
0.84 
13,912 
398 
60 
1,759 
24 
194.9 
6.69 
3.18 
555 
3,457 
11.59 

Adjusted  tonnage  per  train,  average  

Speed  when  train  was  in  motion,  miles  per  hour,  average  . 
Boiler  pressure  when  using  steam  (200  Ib  ),  average  
Front-end  draft  when  using  steam,  in.  of  water,  average.  . 
Firebox  draft  when  using  steam,  in.  of  water,  average  .... 
Temperature  of  steam,  deg.  F  

Ooal  fires  per  hour  of  running  time,  Ib    (average) 

Adjusted  ton-  miles  per  Ib.  of  coal  (average)  

The  locomotive  was  worked  at  its  maximum  capacity 
on  all  trips,  about  10  per  cent  more  tonnage  being  hauled 
than  is  usual  for  like  locomotives  burning  coal  on  grates; 
and  practically  at  fast-freight  schedule  speed.  The  exhaust 
nozzle  opening  was  about  25  per  cent  larger  than  the  maxi- 
mum for  hand  firing. 

The  general  results  were  excellent,  particularly  with 
regard  to  tonnage,  speed,  combustion,  and  steam  pressure, 
the  latter  being  maintained  at  full  speed  with  the  injector 
supplying  the  maximum  amount  of  water  to  the  boiler. 

With  the  highest-sulphur  coal  (No.  1)  and  the  highest- 


176 


POWDERED   COAL  AS  A  FUEL 


ash  coal  (No.  3)  there  was  less  than  1  cu.ft.  of  slag  in  the  slag 
box  at  the  end  of  each  run,  and  practically  no  collection  of 
ash  or  soot  on  the  flue  or  fire-box  sheets.  In  fact,  with  the 


FIG.  69. — Double-Feeder  Equipment  for  Locomotive  Fender, 
N.  Y.  C.  R.  R. 


No.  3  fuel  there  were  less  than  two  handfuls  of  slag,  ash  and 
soot  collected  on  each  trip. 

Demands  upon  steam  railway  motive  power  to  produce 
increased  horse  power  per  hour  are  becoming  more  exact- 
ing, and  there  is  but  little  doubt  that,  through  the  use  of 
powdered  coal  in  combination  with  correlated  improvements 
in  locomotive  design,  the  steam  locomotive  can  be  made  to 


POWDERED  COAL  FOR  LOCOMOTIVES  177 

remain  the  standard  unit  of  motive  power  for  present  and 
future  general  railway  operation,  by  reason  of  its  general 
dependability,  flexibility,  effectiveness,  and  economy,  and 
its  ability,  in  a  revised  form,  to  meet  public  demands  for  the 
reduction  of  smoke,  soot,  cinders,  sparks  and  noise. 


CHAPTER  X 
EXPLOSIONS 

MUCH  has  been  said  of  the  danger  of  explosions  accom- 
panying the  use  of  powdered  coal.  This  is  partly  due  to 
confusion  with  dust  explosions  in  coal  mines.  The  latter 
are  due  to  the  floating  of  dust  in  the  air  in  a  confined  space. 
The  department  of  a  powdered  coal  plant  in  which  the  coal 
grinding  is  done  is  usually  a  fit  place  for  an  explosion,  for 
it  is  almost  impossible  to  grind  coal  without  having  some  dust 
escape.  There  is,  on  the  other  hand,  plenty  of  opportunity 
for  change  of  air,  which  should  minimize  the  possibility  of 
explosions.  Dust  is  sometimes  overcome  by  the  use  of  a 
grinding  system  employing  exhaust  fans.  With  the  atmos- 
phere saturated  with  coal  dust,  and  all  crevices  and  ledges 
filled  and  covered  with  fine  particles,  there  would  seem  to  be 
every  chance  for  an  explosion.  Yet  the  author  has  not 
heard  of  an  instance  where  explosions  have  taken  place  in 
the  grinding  room.  There  have  been  cases  where  a  match 
or  spark,  coming  in  contact  with  some  of  the  dust  lying  on  a 
ledge,  has  started  a  fire  which  has  spread  rapidly,  but  this 
scarcely  constitutes  an  explosion.  The  dust  acts  like  a 
long  fuse.  The  remedy  seems  to  be  to  keep  the  grinding 
room  as  clean  as  possible,  forbidding  the  use  of  any  open 
lights  or  fire. 

During  one  of  the  writer's  inspection  trips  special  inquiry 
was  made  regarding  explosions.  None  had  occurred  at 
any  of  the  plants  visited.  In  certain  cases  the  bins  over- 
flowed and  the  falling  sheet  of  coal  took  fire,  but  there  was 
nothing  that  could  properly  be  called  an  explosion. 

Mr.  W.  D.  Wood,  in  the  Railroad  Gazette  of  July  18, 
1913,  says  of  powdered  coal  explosions: 

"  I  can  say  positively  that  there  is  absolutely  no  danger 

178 


EXPLOSIONS 


179 


180 


POWDERED  COAL  AS  A  FUEL 


EXPLOSIONS 


181 


I 


02 

H 

«f 

I 

r° 
h=H 


1 

I 


182 


POWDERED  COAL  AS  A  FUEL 


of  explosions  of  powdered  coal  where  ordinary  sensible 
precautions  are  observed.  The  writer  has  worked  in  cement 
mills,  and  has  burned  powdered  coal  himself,  and  knows 
whereof  he  speaks.  In  the  first  place,  powdered  coal  when 
in  storage  or  in  bulk,  or  while  being  blown  into  the  furnace, 
does  not  explode.  It  may  puff,  or  flare  back  slightly,  when 
starting  up  a  fire  in  a  furnace,  if  there  is  not  enough  draft, 


24-%  "Holes 

Exhaust  Pipe  from 
Steam  Turbine 


FIG.  73. — Locomotive  Front  End  for  Powdered  Coal. 

but  even  this  is  preventable.  There  have  been  so-callea 
explosions  of  powdered  coal,  several  of  them,  but  not  one 
person  in  ten  has  any  idea  of  what  they  are  like.  Several 
of  the  large  cement  companies,  including  the  Atlas,  Alpha, 
Edison,  and  others,  have  had  explosions,  but  every  one  of 
them  to  my  knowledge  has  originated  in  the  grinding  room 
where  the  coal  was  pulverized.  They  are  sometimes 
caused  by  a  nail  getting  in  the  mill  and  causing  a  spark; 


EXPLOSIONS 


183 


and  sometimes  by  the  presence  of  an  open  flame  when 
cleaning  or  repairing  a  mill. 

"  All  of  these  explosions  are  caused  by  impalpably  fine 
dust  floating  in  the  air  in  suspension.  This  dust  floats  in 
layers  or  strata.  Nails  and  other  pieces  of  iron  should  be 
removed  by  an  electro-magnet  before  the  coal  goes  to  the 
mill,  even  if  only  to  protect  the  mill  from  damage.  At  a 


nti 

"3SHS. 

I 

l'lf"  ANGLE  VALVE 

2 

PRESS  RED.  VAL  V£/k  'INLET- 
1'^'  OUTLET            * 

2 

EXTENSION  HANDLE 

4 

1  ''j"  GLOBE  VALVE 

5- 

l"xix%"  TEE 

6 

300  L8.  DUPLEX  6A&E 

7 

1'^"  QUICK  OPEN.  BLOW  EH 

a 

DAHPER  CONTROLLER  VAL  V? 

9 

FEEDER  CONTROL 

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6RAD.  PRESS.  RED.  VAL  VE 
1"  INLET-  /"OUTLET. 

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17 

GAGE  CONNECTION 

18 

3'4RCD 

19 

BOILERGA6E 

20 

l'<t"xl^"j(l^"TEE 

71 

1%'SLOBE  VALVE 

72 

I^'DIAH.  PIPE 

23 

FURNACE  DOOR 

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TACHOMETER 

25 

t!$"xl"xl"TEE 

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27 

l'l  STEAM  STRAINER 

25 

STa£2ttKs™H 

23 

DOUBLE  RADI  A  TOR  SYPHON  AND 

j!  To  Feeder.- • 
jj  Turbine 

FIG.  74. — Locomotive  Cab  Equipment  for  Powdered  Coal. 

recent  explosion  (?)  in  one  of  the  big  cement  mills  the  facts 
were  as  follows:  A  foreman  and  some  of  his  men  were 
repairing  and  cleaning  a  mill.  One  of  the  men  had  rammed 
a  piece  of  waste  on  the  end  of  a  stick  into  a  part  he  was 
cleaning  and  somehow  (no  one  knows  how)  it  caught  fire 
as  he  pulled  it  out.  Immediately  there  was  a  swift  hissing; 
sound  like  a  pinwheel  going  off,  or  like  escaping  steam,  and  in 


184  POWDERED  COAL  AS  A  FUEL 

a  flash  this  traveled  the  length  of  the  room  down  a  stairway, 
and  back  several  times  in  layers  just  like  a  train  of  powder, 
only  there  was  no  report,  no  explosion,  just  a  hissing. 
The  men  came  out,  they  were  absolutely  denuded,  yet  seemed 
to  retain  then:  faculties.  The  foreman  said  "  I'm  done  for 
and  am  going  to  die."  He  was  able  to  tell  what  had  hap- 
pened before  he  became  unconscious.  They  all  died  shortly 
afterward. 

"  As  terrible  as  this  seems,  it  is  entirely  preventable.  I 
have  never  seen  a  cement  mill  yet  where  you  could  go  near 
the  pulverizing  plant,  much  less  in  it,  without  becoming 
covered  with  coal  dust.  Yet  at  the  American  Iron  and 
Steel  Manufacturing  Co.  works  at  Lebanon,  they  have 
used  powdered  coal  for  ten  years  and  have  never  had  an 
explosion.  I  have  stood  inside  of  their  grinding  room  and 
had  a  white  handkerchief  on  my  sleeve  and  it  caught  not  a 
grain  of  dust. 

"  Cement  mills  seem  to  think  that  it  is  cheaper  to  take 
chances  as  long  as  things  keep  running  rather  than  to  spend 
enough  money  for  safety.  There  are  two  ways  to  be  safe — 
use  a  mill  that  is  tight,  and  spend  enough  money  for  com- 
petent labor  and  materials  to  keep  it  in  repair.  As  to 
storage  and  burning:  coal  pulverized  and  stored  in  tanks  is 
100  per  cent  less  liable  to  explosion  than  oil.  It  sometimes 
catches  fire  from  spontaneous  combustion  or  otherwise, 
and  nothing  happens  any  more  than  what  would  happen 
if  a  pile  of  slack  coal  should  catch  fire.  It  is  not  even  neces- 
sary to  shut  down.  All  that  is  necessary  is  to  keep  right  on 
drawing  it  off  in  its  semi-burnt  state,  cutting  off  the  supply 
to  the  bin  that  is  on  fire,  and  burn  it  until  it  is  all  out  of 
the  tank;  when  a  new  supply  may  be  put  in,  if  the  tank  has 
not  become  heated.  Care  must  be  taken  to  see  that  none 
of  the  burnt  coal  remains. 

"  In  a  large  cement  mill,  where  the  writer  was  employed, 
it  was  frequently  necessary  to  walk  along  the  iron  gallery 
in  front  of  the  supply  bins.  This  gallery  is  practically 
right  over  the  front  end  of  the  kilns  and  only  8  ft.  above 


EXPLOSIONS 


185 


Sectional  Elevation 
A-A 


Pulverized    / 
Fuel*      / 
Controller* 


75. — Powdered  Coal  Equipment  for  Stirling  Boiler.  The  Hudson  Coal  Co. 


186  POWDERED  COAL  AS  A  FUEL 

them.  The  coal  dust  which  has  overflowed  the  bins  is  always 
from  2  to  4  in.  thick  on  this  walk.  Even  when  careful 
(which  no  one  is)  a  person  kicks  showers  of  this  fine  dust 
right  down  over  the  open  red-hot  end  of  the  kilns;  it  is 
sometimes  kicked  down  over  a  new  man  as  a  joke.  Clouds 
of  this  dust  drift  down  over  the  kilns  and  are  sucked  in  by 
the  draft.  Certainly  no  severer  test  than  this  could  be 
applied. 

"  Powdered  coal  is  as  safe  as  coal  in  lumps,  if  common 
sense  and  judgment  are  exercised,  and  any  one  who  believes 
the  contrary  is  laboring  under  a  misunderstanding  of  the 
facts  in  the  case. 

"  Open  dryers  should  not  be  used,  that  is  dryers  in  which 
the  heat  and  flame  come  in  direct  contact  with  the  coal. 
This  is  dangerous  and  should  not  be  tolerated,  though  some 
concerns  practice  it.  There  are  plenty  of  good  compart- 
ment dryers  on  the  market  which  are  safe." 

In  1915  Mr.  Thomas  A.  Edison,  in  explanation  of  the  so- 
called  explosion  that  took  place  in  his  cement  mill  some 
years  ago  made  the  following  statement:  "  The  explosion 
was  occasioned  by  fine  coal  dust  catching  fire  and  burning 
slowly  in  a  pit,  thus  forming  an  explosive  gas  with  the  air. 
The  explosion  killed  five  men.  Please  let  me  emphasize 
the  fact  that  it  was  not  the  dust  itself  that  exploded." 

Another  view  of  explosions:  "  With  regard  to  explosions, 
powdered  coal  is  much  safer  than  oil  or  natural  gas,  as  a 
leak  is  at  once  detected  by  the  eye,  and  the  trouble  can  be 
remedied  immediately.  The  entire  system,  from  the  point 
where  the  coal  is  dried,  to  the  bins  at  the  furnaces,  may  be 
entirely  enclosed,  rendering  it  absolutely  dust-tight.  The 
bins  and  conveying  system  contain  but  a  small  quantity 
of  air;  and  an  explosion  there  is  absolutely  impossible  in  a 
well-designed  plant." 

One  large  company  in  the  central  part  of  New  York 
State,  in  stating  their  experience,  say  "  We  never  had  an 
explosion  from  the  use  of  powdered  coal  and  we  have 
made  extensive  experiments  with  it.  We  do  not  consider 


EXPLOSIONS 


187 


188  POWDERED  COAL  AS  A  FUEL 

it  advisable  to  have  large  quantities  of  powdered  coal 
lying  around." 

Storage  Difficulties.  Storage  difficulties  should  not  exist 
with  dry  coal.  There  should  be  no  floating  dust  in  the  at- 
mosphere. Moist  coal  should  not  be  stored  as  it  does  not 
flow  freely,  but  cakes  up  and  gives  trouble.  Provision 
should  be  made  for  keeping  the  coal  moving,  and  in  case  of 
shut-down  of  plant,  coal  should  not  be  left  in  the  storage 
bins  for  much  over  a  week.  These  are  the  only  precautions 
which  it  is  necessary  to  take.  No  trouble  is  experienced 
from  the  storage  of  coal  for  short  periods  of  time.  It  should 
be  given  a  chance  to  cool  between  the  pulverizing  machine 
and  the  storage  bin. 

The  caking  of  coal  dust  in  separate  bins  at  each  furnace 
was  the  cause  of  a  fire  at  the  Burden  Iron  Works  about 
two  years  ago.  The  coal  persisted  in  caking  and  the  men 
were  in  the  habit  of  using  a  club  to  hammer  the  sides  of  the 
bins  in  order  to  get  the  coal  dust  to  flow  into  the  controller, 
until  the  point  was  reached  where  the  bins  were  getting  so 
damaged  that  the  manager  had  to  forbid  hammering. 
Then  one  night  one  of  the  men,  trying  to  get  coal  dust, 
removed  the  slide  at  the  bottom  of  the  bin  between  it  and  the 
controller,  thinking  no  doubt  that  the  coal  would  then  move 
more  freely,  with  the  result  that  the  coal  dust  leaked  in 
small  particles  down  on  to  the  floor.  There  was  a  strong 
wind  blowing  at  the  time,  and  just  at  the  moment  when  the 
operator  was  taking  out  a  heat,  a  puff  of  wind  blew  some  of 
the  coal  dust  across  the  heat  with  the  result  that  it  instantly 
took  fire.  The  conditions  here  were  ideal  for  combustion. 

It  was  a  coincidence  that  just  above  this  furnace  the  shop 
was  divided  into  two  parts,  the  old  one  having  a  roof  of  wood 
trusses  and  the  new  part  one  of  steel  trusses.  The  flame 
shot  up  instantly  to  the  wood  trusses  and  as  they  were 
covered  with  fine  particles  of  powdered  coal  the  fire  swept 
across  these  trusses  and  inside  of  ten  minutes  the  roof  was  a 
furnace  and  the  men  had  to  flee  for  their  lives.  The  fire 
burned  from  10  P.M.  to  2  A.M.,  when  the  roof  all  caved  in 


EXPLOSIONS 


189 


190  POWDERED  COAL  AS  A  FUEL 

and  fell  on  the  furnaces.  That  part  of  the  building  having 
the  steel  trusses  did  not  catch  fire,  thanks  to  the  efforts  of  the 
firemen.  The  measuring  hoppers  and  screw  conveyors, 
with  walkways,  came  down  with  the  roof,  but  there  was  no 
back  flash  of  coal  dust  through  the  conveyors,  nor  was  there 
any  explosion  of  coal  dust.  It  was  simply  a  fire  caused  by  the 
existence  of  perfect  conditions  for  combustion. 


BIBLIOGRAPHY 

LIST  OP  REFERENCES  COMPILED  BY  ENGINEERING  SOCIETIES 

LIBRARY 

FUEL  POSSIBILITIES  IN  STEEL  MAKING.  Iron  Age,  November  6,  1913, 
p.  1056-1059.  Paper  read  before  the  American  Iron  and  Steel  Insti- 
tute, by  William  Whigham.  The  author  discusses  the  use  of  pul- 
verized coal  as  a  fuel  for  open-hearth  furnaces. 

IMPROVED  PULVERIZED  FUEL  FEED  DEVICE.  Iron  Age,  November  6, 
19i3,  p.  1024.  Brief  description  of  the  Dunn  apparatus,  especially 
intended  for  cement  kilns,  but  used  also  in  the  nodulizing  of  iron  ore. 

WIDER  UTILIZATION  OF  PULVERIZED  COAL,  H.  R.  Barnhurst.  Iron  Age, 
October  23,  1913,  p.  906-908.  Part  of  discussion  of  paper  by  James 
Lord  on  The  Use  of  Pulverized  Fuel  in  Metallurgical  Furnaces,  read 
before  the  Engineers'  Society  of  Western  Pennsylvania. 

POWDERED  COAL  FOR  OPEN  HEARTH  FURNACES.  Iron  Age,  October  16, 
1913,  p.  855.  Abstract  from  the  "  Coal  and  Coke  Operator." 

USE  OF  PULVERIZED  COAL  AS  A  FUEL  FOR  BOILERS,  R.  C.  Carpenter. 
Sibley  Journal  of  Engineering,  December,  1913,  p.  85. 

COAL-DUST  FIRED  BOILER.  Indian  Engineering,  November  29,  1913, 
p.  301. 

PROGRESS  IN  FUEL  UTILIZATION.  Mining  and  Scientific  Press,  October 
25,  1913,  p.  638. 

BUFFALO  GRAIN  ELEVATOR  DUST  EXPLOSION.  Engineering  News,  July 
31,  1913,  p.  223-24.  Reprinted  in  the  National  Fire  Protection 
Association  Quarterly,  October,  1913,  p.  149-151.  Mention  is  made 
of  the  danger  of  explosions  in  connection  with  the  burning  of  pow- 
dered coal. 

POWDERED  FUEL  AND  EXPLOSIONS.  Railway  Age  Gazette,  July  18,  1913, 
p.  83-84.  Letter  by  W.  D.  Wood. 

USE  OF  PULVERIZED  COAL  IN  METALLURGICAL  FURNACES,  James  Lord. 
Engineers'  Society  of  Western  Pennsylvania,  Proc.,  October,  1913, 
p.  363-372;  discussion,  p.  371-417.  With  bibliography. 

PULVERIZED  FUEL  FOR  BOILER  FIRING,  C.  H.  Wright.  Electrical  World, 
March  15,  1913,  p.  567-569. 

PULVERIZED  COAL  AS  A  FUEL,  H.  R.  Barnhurst.  Metallurgical  and  Chem- 
ical Engineering,  March,  1913,  p.  127-129.  With  special  reference 
to  metallurgical  furnaces. 

191 


192  POWDERED  COAL  AS  A  FUEL 

POWDERED  COAL  AS  FUEL.  Indian  Engineering,  August  16,  1913,  p.  91. 
Briefly  discusses  its  use  as  a  locomotive  fuel. 

POWDERED  FUEL  FOR  LOCOMOTIVES,  Walter  D.  Wood.  Railway  Age 
Gazette,  July  4,  1913,  p.  13-15;  Aug.  1,  p.  174. 

PULVERIZED  COAL  AS  A  CHEAP  FUEL.  Automobile,  June  5,  1913,  p.  1177. 
Letter  asking  questions  as  to  the  use  of  pulverized  coal.  Answers 
are  given. 

PROBLEM  OF  BURNING  PULVERIZED  FUEL,  Sterling  H.  Bunnell.  Iron 
Age,  September  18,  1913,  p.  618. 

USE  OF  PULVERIZED  COAL  AS  FUEL  FOR  METALLURGICAL  FURNACES, 
H.  R.  Barnhurst.  American  Institute  of  Mining  Engineers,  Bull., 
October,  1913,  p.  2523-2532;  discussion,  December,  1913,  p.  2856- 
2863. 

PULVERIZED  COAL  AS  A  FUEL,  A.  W.  Raymond.  Metallurgical  and 
Chemical  Engineering,  February,  1913,  p.  108-109.  On  the  use  of 
pulverized  coal  in  metallurgical  furnaces  and  in  cement  burning. 

BURNING  OF  POWDERED  COAL,  W.  E.  Porter.  Industrial  World,  vol. 
47,  p.  146-147,  February  3,  1913. 

POWDERED  COAL  AS  FUEL,  W.  S.  Quigley.  Railway  and  Engineering 
Review,  November  15,  1913,  p.  1067-1068.  Paper  read  before  the 
American  Foundrymen's  Association. 

SMALL  COAL  AND  DUST:  ITS  PRODUCTION,  PREVENTION,  TREATMENT,  AND 
UTILIZATION,  WITH  SPECIAL  REFERENCE  TO  DRY  MINES,  J.Drummond 
Paton.  Institution  of  Mining  Engineers,  Trans.,  vol.  45,  pt.  3, 
p.  421-446;  discussion,  p.  446-449,  1912-1913.  Same  in  Manches- 
ter Geological  and  Mining  Society,  Trans.,  vol.  33,  pt.  6,  p.  198-223; 
discussion,  p.  223-226,  1912-1913.  Results  of  official  tests  made  by 
the  Stirling  Boiler  Co. 

FIRING  SOFT  COAL  SCREENINGS,  John  S.  Leese.  Mechanical  World, 
vol.  51,  p.  160-161,  1912. 

DUST  FUEL  BOILER  AND  ITS  USES,  H.  V.  Hart  Davis.  Manchester  Geo- 
logical and  Mining  Society,  Trans.,  vol.  22,  p.  224-233;  discussion, 
p.  233-242, 1912.  Abstract  in  Iron  and  Coal  Trades  Review,  February 
23, 1912,  p.  198-299;  Engineering  Magazine,  March,  1913,  p.  936-938. 

PULVERIZED  COAL  AN  ECONOMICAL  STEAM  FUEL.  Steam,  May,  1912, 
p.  135-138.  A  table  shows  results  obtained  with  a  Bettington  boiler. 

METHODS  OF  BURNING  ANTHRACITE  COAL  DUST,  Wm.  Kavanagh.  Elec- 
trical World,  December  7,  1912. 

RECENT  IMPROVEMENTS  AND  ADDITIONS  TO  THE  SMELTING  PLANT  OF  THE 
CANADIAN  COPPER  COMPANY,  D.  H.  Browne.  Canadian  Mining 
Institute,  Trans.,  vol.  15,  p.  115-122, 1912. 

COMBUSTION  OF  PULVERIZED  COAL,  L.  S.  Hughes.  American  Institute 
of  Chemical  Engineers,  Trans.,  vol.  4,  p.  347-349,  1911. 


BIBLIOGRAPHY  193 

PULVERIZED  COAL,  A  NEW  FUEL,  Wm.  D.  Ennis.    Automobile,  vol.  25, 

p.  620-621,  1911.     Contains  paragraph  on  the  use  of  powdered  coal 

under  steam  boilers. 
BETTINGTON  BOILERS  FOR  PULVERIZED  FUEL.    Railway  News,  vol.  96, 

p.  1422-1423,  1911.     Gives  results  of  tests. 
DE  L'EMPLOI  DBS  POUSSIERS  DANS  LES  FOYERS  MECANIQUES,  J.  Izart. 

L'Electricien,  vol.  41,  p.  54-57,  1911. 
FIRING  BOILERS  WITH  PULVERIZED  COAL,  W.  S.  Worth.    Power,  vol.  33, 

p.  264-267,  1911.    Tests  were  made  at  the  Henry  Phipps  plant, 

Pittsburg. 

THE  ROTARY  KILN,  Ellis  Soper.    American  Society  of  Mechanical  Engi- 
neers, Journal,  October,  1910;  discussion,  April,  1911.     In  the  paper 

and  in  the  discussion  reference  is  made  to  the  earliest  successful  use  of 

pulverized  coal  for  cement  manufacture. 
USE  OF  PULVERIZED  COAL  FOR  FOUNDRY  PURPOSES,  Richard  K.  Meade. 

American   Foundrymen's    Association,    Trans.,    vol.    18,    p.    39-45, 

1909.    Abstract  in  Foundry,  vol.  34,  p.  196-198,  1909.    The  author 

gives  an  estimate  of  the  cost  of  pulverizing. 
COAL  DUST  FIRING  OF  REVERBERATORY  FURNACES,  Edward  G.  Thomas. 

Engineering  and  Mining  Journal,  vol.  85,  p.  269-270,  1908. 
COAL  DUST  FIRING  FOR  REVERBERATORY  FURNACES,  Charles  F.  Shelby. 

Engineering  and  Mining  Journal,  vol.  85,  p.  541-544,  1908. 
FEEDING  PULVERIZED  COAL  TO  FURNACES,  R.  Cederblom.    Power,  vol. 

28,  p.  299-300,  1908. 
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Brooklyn  Engineers'  Club,  Proc.,  vol.  12,  p.  183-200;   discussion,  p. 

201-217,  1908.    The  author  discusses  various  methods  of  grinding 

coal  and  special  applications  such  as  firing  of  steam  boilers  and 

industrial  furnaces. 
PULVERIZED  COAL   AND  ITS  INDUSTRIAL  APPLICATIONS,  W.  D.  Ennis. 

Engineering  Magazine,  vol.  34,  p.  463,  577,  1907-1908.     Costs  are 

given. 
USE  OF  PULVERIZED  FUEL  FOR  HEATING  METALLURGICAL  FURNACES, 

Richard    K.    Meade.    American   Institute   of   Chemical   Engineers, 

vol.  1,  p.  98-115,  1908. 

USING  SOFT  COAL  SCREENINGS.    Power,  vol.  29,  p.  706,  1908. 
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ical Engineers,  Trans.,  vol.  29,  p.  143-148;   discussion,  p.  149-158, 

1907.     In  the  discussion  Prof.  William  D.  Ennis  gives  some  figures 

relative  to  the  cost  of  pulverizing  coal. 
SCHWARTZKOPFF  SYSTEM  OF  COAL  DUST  FIRING,  P.  M.  Pritchard.     Liver- 

pool  Engineering  Society,  Trans.,  vol.  28,  p.  154-165;   discussion,  p. 

166-176,  1907.    An  account  of  tests. 


194  POWDERED  COAL  AS  A  FUEL 

DUST  FUEL  STOCKERS  AND  AUXILIARY  PLANT,  W.  R.  Harrison.  Leeds 
University  Society,  December  10,  1906. 

BAENSCH-FEUERUNGEN  ZUR  VERFEUERUNG  VON  TEER,  KOHLENSTAUB, 
ETC.,  Wegener.  Asphaltkunde  u.  Teer  Industrie  Zeitung,  vol.  6,  p.  4, 
1906. 

COAL  PULVERIZER  AND  AUTOMATIC  STOKER.  American  Electrician, 
vol.  14,  p.  196-197,  1906.  Description  of  "  Ideal  "  fuel  feeder. 

POWDERED  COAL  FIRING  FOR  STEAM  BOILERS,  Geo.  C.  McFarlane. 
Engineering  and  Mining  Journal,  vol.  81,  p.  901-902,  1906.  Com- 
parison of  costs  of  hand  firing  and  powdered-coal  firing. 

PROBLEM  OF  SMOKE  ABATEMENT,  Wm.  H.  Bryan.  American  Machinist, 
vol.  29,  pt.  2,  p.  52-54,  1906.  Powdered  coal  is  compared  with 
other  fuels,  as  to  cost,  efficiency. 

COAL  DUST  FIRING  OF  REVERBERATORY  MATTE  FURNACES,  S.  Severin 
Sorensen.  Engineering  and  Mining  Journal,  vol.  81,  p.  274-276. 
1906.  With  diagrams  of  smelting  results. 

COAL  DUST  FIRING  FOR  STEAM  BOILERS.  Engineer  (Lond.),  vol.  99, 
p.  502-503,  1905.  Gives  results  of  tests  made  with  the  Schwartzkopff 
apparatus  by  C.  E.  Stromeyer,  of  the  Manchester  Steam  Users' 
Association. 

FIRING  WITH  COAL  DUST,  Eustace  Carey.  Society  of  Chemical  Industry, 
Jour.,  vol.  24,  p.  369-371;  discussion,  p.  371-372,  1905.  Abstract 
in  Engineering  and  Mining  Journal,  vol.  80,  p.  1113-1114,  1905. 

UTILIZATION  OF  LOW-GRADE  FUELS  FOR  STEAM  GENERATION,  W.  Francis 
Goodrich.  Engineering  Magazine,  vol.  30,  p.  346-354,  1905. 

ROAD  TESTS  OF  BROOKS  PASSENGER  LOCOMOTIVES,  E.  A.  Hitchcock. 
American  Society  of  Mechanical  Engineers,  Trans.,  vol.  26,  p.  290- 
306;  discussion,  p.  306-311,  1905.  In  the  discussion  on  pp.  310- 
311  the  use  of  pulverized  coal  as  a  fuel  for  locomotives  was  con- 
sidered. 

COAL  DUST  FIRING  AS  APPLIED  TO  ANNEALING  FURNACES.  Iron  and  Coal 
Trades  Review,  vol.  70,  p.  1999,  1905.  Schwartzkopff  system. 

COMPARATIVE  BOILER  TESTS  WITH  ORDINARY  AND  PULVERIZED  COAL 
FIRING.  Engineering  Record,  vol.  49,  p.  342,  1904. 

BURNING  POWDERED  COAL,  H.  J.  Travis.  Power,  vol.  24,  p.  168-196, 
271,  1904.  Tests  of  various  systems,  also  comparative  tests  of 
hand-fired  and  pulverized-fuel  boilers. 

POWDERED  COAL  FOR  STEEL  ANNEALING,  H.  J.  Travis.  American 
Machinist,  vol.  27,  pt.  1,  p.  791-792,  1904. 

USE  OF  PULVERIZED  COAL  FOR  FUEL  UNDER  STEAM  BOILERS,  J.  M.  Swee- 
ney. Western  Society  of  Engineers,  Jour.,  vol.  9,  p.  141-149;  dis- 
cussion, p.  149-160,  1904.  With  tables,  showing  evaporation 
secured  from  pulverized  fuel  and  hand-fired  coal. 


BIBLIOGRAPHY  195 

TEST  OF  PULVERIZED  FUEL.    Engineer  (U.  S.),  vol.  41,  p.  259-260, 

1904.    Tests  were  made  at  the  plant  of  the  International  Harvester 

Company. 

BURNING  OF  PULVERIZED  COAL,  C.  0.  Bartlett.    Association  of  Engineer- 
ing Societies,  Jour.,  vol.  31,  p.  44-48,  1903;  Railway  and  Engineering 

Review,  vol.  43,  p.  568-569, 1903;  Engineer  (U.  S.),  vol.  50,  p.  563-564, 

1903.     Paper  read  before  the  Civil  Engineers'  Club  of  Cleveland. 

Gives  estimated  cost  of  outfit  for  about  40  tons  per  day  of  ten  hours. 
BURNING  POWDERED  COAL  UNDER  BOILERS.    Power,  vol.  23,  p.  434-437, 

1903. 

POWDERED  FUEL.     Power,  vol.  23,  p.  561,  1903.     Letter  by  W.  E.  Crane. 
PULVERIZED  FUEL.     Engineer  (U.  S.),  vol.  40,  p.  272-275,  1903.     Costs 

are  given  and  an  estimate  of  the  saving  made  by  pulverizing  the 

coal. 
IMPROVED  SYSTEM  OF  BURNING  COAL  DUST.    Engineer  (U.  S.),  vol.  40, 

p.  93-94,  1903.     The  Rowe  system. 
A  ROTARY  BRUSH  SYSTEM  OF  FEEDING  PULVERIZED  FUEL  TO  FURNACES. 

Engineering  News,  vol.  47,  p.   147,   1902.     Test  of  Schwartzkopff 

system. 
SYSTEM  FOR  BURNING  COAL  DUST.    American  Miller,  vol.  30,  p.  1006, 

1902.    Bartlett  and  Snow  system. 
UEBER    DEN    GEGENWAERTIGEN    STAND    DER    KOHLENSTAUBFEUERUNG, 

Haeussermann.     Gewerblich  technischer  Ratgeber,  vol.  1,  p.  227-229, 

1902. 
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p.  10-12. 

PULVERIZED  FUEL  FOR  POWER  PLANTS,  Gasche  (Aero  Pulverizer).     Rail- 
road Gazette,  vol.  34,  p.  446-467,  1902.     Gives  summary  of  results 

of  boiler  trials. 
KESSELFEUERUNG  MIT  PULVERISIERTER  KOHLE  ("  Pulverisator  cyclon," 

"  Aero-Pulverisator  ").     Leipziger  Monatsschrift  fur  Textil  Industrie, 

vol.  17,  p.  479,  1902. 
A  NEW  SYSTEM  FOR  BURNING  POWDERED  COAL.    Engineering  News,  vol. 

48,  p.  548,  1902.     Rowe  and  Bender  system. 
THE  ROWE  SYSTEM  OF  BURNING  PULVERIZED  COAL.     Engineering  Record, 

vol.  46,  p.  592,  1902. 
PULVERIZED  COAL  BURNING  IN  CHICAGO.     American  Electrician,  vol.  14, 

p.  13-14,  1902. 
PULVERIZED  FUEL  FOR  POWER  PLANTS.     Railroad  Gazette,  vol.  24,  p. 

466-467,  1902.     With  tables  giving  summary  of  results  of  boiler 

trials,  and  heat  balance  for  dust  fuel  test. 
KOMBINIERTE  KOHLENSTAUBFEUERUNG.    Zeitschrift  fur  Beleuchtungswesen 

vol.  7,  p.  332-333,  1901. 


196  POWDERED   COAL  AS  A  FUEL 

KOHLENSTAUBFEUERUNGEN,  Ruhl.    Kraft,  vol.  18,  pt.  1,  p.  35-37,  1901. 
POWDERED  FUEL  FOR  BOILER  FURNACES  AT  THE  ALPHA  CEMENT  COM- 
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1901. 
A  NEW  METHOD  OF  BURNING  POWDERED  FUEL.    Engineering  News,  vol. 

45,  p.  178-179,  1901.     Description  of  Westlake  system,  with  results 

of  tests. 
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Record,  vol.  43,  p.  506,  1901. 
PULVERIZED  FUEL,  R.  A.  Douglas.    American  Electrician,  vol.   13,  p. 

434-435,  1901. 
Two  RECENT  SYSTEMS  FOR  BURNING  POWDERED  COAL.    Engineering 

News,    vol.  46,  p.  415-416,  1901.     Cyclone    and    Aero    Pulverizer 

systems. 

FREITAG'S  KOHLENSTAUB-FEUERUNG.    Kraft,  vol.  17,  p.  5-6,  1900. 
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242,  1900.     Editorial  note  on  the  use  of  pulverized  coal  in  rotary 

cement  kilns. 
BURNING  PULVERIZED  COAL.    Railway  and  Engineering  Review,  vol.  40, 

p.  560-562,  1900. 
BURNING  POWDERED  COAL  IN  STATIONARY  BOILERS.    Engineering  Record, 

vol.  42,  p.  615-616,  1900.    Tests  with  Westlake  apparatus. 

EMPLOI   DU   CHARBON   PULVERISE   DANS   LES   FOYERS   DES   CHAUDIERES   ET 

DBS  FOURS  METALLURGIQUE  (systeme  Schwartzkopff ) ,  A.  Halleux. 

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Coal  Trades  Review,  vol.  58,  p.  643,  1899. 
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des  Vereines  deutscher  Ingenieure,  vol.  43,  p.  988-992,  1899. 
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vol.  77,  p.  477,  1899.    Abstract  from  Neues  Saarbrueckener  Gewerbe- 

blatt. 
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p.  542-543,  1899.     Abstract  of  article  by  L.  Kaufmann  in  Zeitschrift 

des  Vereines  deutscher  Ingenieure. 
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vol.  22,  p.  101,  1899. 
UEBER    VERWERTHUNG    VON    KOHLENSCHLAMM    UND    KOHLENSTAUB. 

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1898-1899. 


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vol.  38,  p.  189-190,  1897.     Wegener  system. 
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198  POWDERED  COAL  AS  A  FUEL 

1896.    Experiments  made  by  Mr.  Bryan  Donkin  with  the  Wegener 

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FRIEDEBERG.    Dampf,  vol.  13,  p.  502,  1896. 
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Friedrich.    Dampf,  vol.  13,  p.  710,  1896. 
APPARATOS   PARA   LA   COMBUSTION   DE   CARBONES   MENUDOS,   Colomer. 

Revista  Minera,  vol.  45,  p.   175,   1895.    Wegener,  Friedberg  and 

SchwartzkopfT  systems. 

DIE  NEUEREN  KOHLENSTAUBFEUERUNGS-APPARATE,  B.  KoSHiann.      Stahl 

und  Eisen,  vol.  15,  p.  235-242,  1895. 
DIE  KOHLENSTAUBFEUERUNG,  Schneider.    Zeit.  des  Verbandes  der  Dampf- 

kessel  Ueberwachungs-Vereins,  vol.  18,  336,  1895. 
KOHLENSTAUBFEUERUNGEN,  Schrey.    Glaser's  Annalen  fur  Gewerbe  und 

Bauwesen,  vol.  36,  p.  213-219;  discussion,  p.  219-220,  1895.    Paper 

read  before  the  Verein  deutscher  Maschinen  Ingenieure. 


BIBLIOGRAPHY  199 

KOHLENSTAUBFEUERUNGEN    VON    SCHWARTZKOPFF.       Oest.    Zeitschnft  fur 

Berg  und  Huttenwesen,  vol.  43,  p.  187-188,  1895. 
DIE  SCHWARTZKOPPFF'SCHE  KOHLENSTAUB  FEUERUNG,  Schneider.    Zeit. 

Verband  Dampfkessel  Ueberwach,  Ver.,  vol.  18,  p.  403,  1895. 
VERSUCHSERGEBNISSE  MIT  DER  WEGENER'SCHEN  KOHLENSTAUBFEUERUNG. 

Zeit.  Verband  Dampfkessel  Ueberwach,  Ver.,  vol.  18,  p.  380,  1895. 
KOHLENSTAUBFEUERUNGEN.    Zeit.  des  Vereines  deutscher  Ingenieure,  vol. 

39,  p.  1379-1382,    1895.    Abstract  in  Engineer  (Lond.),    vol.    81, 

p.  106,  1896.     Gives  historical  sketch  of  the  use  of  coal  dust  as 

fuel. 
CHAUFFAGE  DES  CHAUDIERES  AU  CHARBON  PULVERISE  (Systeme  Baumert 

et  Wegener).     Revue  Industrielk,  vol.  25,  p.  62-63,  1894. 
APPAREIL  FRIEDEBERG  POUR  BRULER  LA  POUSSIERE  DE  CHARBON,  G. 

Lestang.    Revue  Industrielk,  vol.  25,  p.  461-462,  1894. 
APPARATUS  FOR  BURNING  COAL  DUST  (Friedeberg  system).     Industries 

and  Iron,  vol.  17,  p.  354,  1894. 
STAUBKOHLENFEUERUNG  (EINRICHTUNG  UND  VERSUCHE  IN  DER  INKRUS- 

TATSEINFABRIK  ZU  PLOETZENSEE).      Dampf,  Vol.  11,  p.  102,  1894. 

UEBER  KOHLENSTAUBFEUERUNGEN.    Dampf,  vol.  11,  p.  509,  1894. 
NEUERE   DAMPFKESSEL  KESSELFEUERUNGEN.    Dingler's  Polytechnische 

Journal,  vol.  291,  p.  241-247,  1894. 
UEBER    KOHLENSTAUBFEUERUNGEN.    Dingler's    Polytechnische    Journal, 

vol.  292,  p.  265-270,  1894. 
FRIEDEBERG  APPARATUS  FOR  BURNING  COAL  DUST.    Industries  and  Iron, 

vol.  17,  p.  405,  1894. 
DIE  KOHLENSTAUBFEUERUNG  PATENTS  FRIEDEBERG,  B.  Kosmann.    Berg 

u.  Huttenmannische  Zeitung,  vol.  53,  p.  371-374,  1894. 
NEUERE  KESSELFEUERUNGEN.    Dingkr's  Polytechnische  Journal,  vol.  287, 

p.  108,  1893. 
KOHLENSTAUBFEUERUNG    VON    BAUMERT    UND    WEGENER.    Dingkr's 

Polytechnische  Journal,  vol.  289,  p.  23, 1893.     Paragraph  on  use  by  the 

North  German  Lloyd  Company. 
MELDRUM  SELF-CONTAINED  DUST-FUEL  FURNACE.  Wm.  Boby.    Federated 

Institution  of  Mining  Engineers,  Trans.,  vol.  3,  p.  250-255,  1891- 

1892. 
STEAM  BOILERS  WITH  FORCED  BLAST:  THE  PERRET  SYSTEM  FOR  BURNING 

DUST  AND  REJECTED  FUELS,  WITH  NOTES  ON  TESTING  BOILERS,  Bryan 

Donkin.     Federated  Institution  of  Mining  Engineers,    Trans.,   vol. 

4,  p.  154-166,  1892-1893.     Discussion  of  papers  by  Wm.  Boby  and 

B.  Donkin,  p.  348-350. 
RAUCHLOSE  KOHLENVERBRENNUNG  (MITTELST  STAUBKOHLE).    Mittheilun- 

gen  aus  dem  Gebiete  des  Seewesens,  vol.  21,  p.  63,  1893. 
FOYERS  DU  SYSTEME  DE  MM.  BAUMERT  ET  WEGENER  POUR  L'UTILISATION 


200  POWDERED  COAL  AS  A  FUEL 

SOUS    LES    CHAUDIERES    DE    CHARBON    PULVERISE.      ReVlM 

des  Mines,  vol.  24,  p.  238-241,  1893. 

UEBER  EINE  NEUE  FEUERUNG  (PATENT  KUDLICZ)  ZUM  VERBRENNEN 
VON  FEINKOHLE,  KOHLENLOESCHE,  SCHLAMMKOHLE,  KOKSKLEIN, 
BRAUNKOHLENABFAELLEN  UND  DERGL,  L.  Glaser.  Glaser's  Annalen 
fiir  Gewerbe  und  Bauwesen,  vol.  33,  p.  31-37,  1893. 

ON  SOME  APPLIANCES  FOR  THE  UTILIZATION  OF  REFUSE  AND  DUST  FUEL, 
Walter  G.  McMillan.  Society  of  Arts,  Journal,  vol.  34,  p.  527-540; 
discussion,  p.  540-542,  1886.  Various  furnaces  are  described,  and 
and  results  of  tests  with  Perret's  boiler  furnace  are  given. 

POWDERED  ANTHRACITE  AND  GAS  FUEL.  Engineering  News,  vol.  16, 
p.  314r-315,  1886.  Abstract  from  report  of  Scranton  Board  of 
Trade. 

PERRET'S  FURNACE  FOR  DUST  FUEL.    Iron  Age,  December  10, 1885,  p.  35. 

ON  THE  CONVERSION  OF  HEAT  INTO  USEFUL  WORK,  William  Anderson. 
Society  of  Arts,  Journal,  vol.  33,  p.  643-656,  1885.  The  author 
describes  Crampton's  system  of  coal-dust  burning  for  a  revolving 
puddling  furnace,  also  the  same  system  adapted  to  marine  boilers. 

THE  UTILIZATION  OF  COAL  DUST  AS  FUEL.  Engineering  News,  vol.  10, 
p.  163,  1883. 

COAL  DUST  FUEL.  Engineer  (Lond.),  vol.  43,  p.  335-336,  1877.  Gives 
results  of  experiments  with  Stevenson's  apparatus. 

ON  THE  USE  OF  PULVERIZED  FUEL,  B.  F.  Isherwood.  Engineering  and 
Mining  Journal,  vol.  21,  p.  12,  31,  57,  104,  129,  1876.  An  account 
of  experiments  made  at  South  Boston,  with  the  Whelpley  and  Storer 
apparatus.  In  addition,  the  author  gives  a  sketch  of  the  history  of 
pulverized  coal  burning,  beginning  with  the  English  patent  of  J.  S. 
Dawes  in  1831. 

NOTES  SUR  LES  DANGERS  QUE  PARAIT  PRESENTER  LA  POUSSIERE  DE 

HOUILLE  DANS  LES  MINES,  MEME  EN  L'ABSENCE  DE  GRISON.      AnnaleS 

des  Mines,  Memoires,  Ser.  7,  vol.  7,  176-179,  1875. 
ON  THE  COMBUSTION  OF  POWDERED  FUEL  IN  REVOLVING  FURNACES, 

AND  ITS  APPLICATION  TO  HEATING  AND  PUDDLING  FURNACES,  T.  R. 

Crampton.    Iron   and   Steel   Institute,   Journal,    1873,    p.    91-101; 

discussion,  p.  101-107. 
ON  THE  USE  OF  PULVERIZED  FUEL,  Lieut.  C.  E.  Dutton.    Franklin 

Institute,  Journal,  vol.  81,  p.  377;   vol.  92,  p.  17,  1871.    Whelpley 

and  Storer  process. 
FOUR  CRAMPTON,  M.  Lavalley,  Societe  des  Ingenieurs  Civils  de  France, 

Memoires,  1875,  p,  266-272;  discussion,  p,  272-278, 


BIBLIOGRAPHY  201 

BOOKS  AND  PAMPHLETS 

BARB,  WILLIAM  M.  A  Practical  Treatise  on  the  Combustion  of  Coal, 
including  descriptions  of  various  mechanical  devices  for  the  economic 
generation  of  heat  by  the  combustion  of  fuel,  whether  solid,  liquid  or 
gaseous.  Indianapolis,  Yohn  Bros.,  1879.  Chapter  14 — Coal  dust 
fuel.  An  account  of  experiments  made  by  the  U.  S.  Government  in 
1876.  Comparative  economy  of  powdered  fuel  as  compared  with 
ordinary  coal.  Stevenson's  apparatus  for  burning  coal  dust. 

BERTIN,  L.  E.  Marine  Boilers.  Translated  and  edited  by  Leslie  S. 
Robertson.  Ed.  2.  New  York,  Van  Nostrand,  1906,  p.  114-120. 

BOURNE,  JOHN.  A  Treatise  on  the  Steam  Engine.  New  York,  Appkton, 
1866,  p.  358.  The  author  considers  that  coal-dust  burning  in  loco- 
motives would  be  feasible,  but  details  had  not  been  worked  out. 

CLARK,  D.  KINNEAR,  editor.  Fuel:  its  combustion  and  economy, 
consisting  of  abridgments  of  "  Treatise  on  the  Combustion  of  Coal 
and  Prevention  of  Smoke,"  by  C.  W.  Williams,  and  "  The  Economy 
of  Fuel,"  by  T.  Symes  Prideaux,  with  extensive  additions  on  recent 
practice  in  the  combustion  and  economy  of  fuel,  coal,  coke,  wood, 
peat,  petroleum,  etc.  Lond.,  Crosby,  Lockwood;  New  York,  Van 
Nostrand,  1879.  Chapter  25— Powdered  Fuel. 

DAMOUR,  EMILIO,  AND  QUENEAU,  A.  L.  J.  Industrial  Furnaces.  New 
York,  Engineering  and  Mining  Journal,  1906,  p.  275-286.  Contains 
list  of  U.  S.  Patents  covering  the  stoking  of  powdered  fuel  to  May  10, 
1904. 

FOWLER,  WILLIAM  H.  Steam  Boilers  and  Supplementary  Appliances. 
Manchester,  Scientific  Pub.  Co.,  p.  491-492,  paragraph  on  dust  fuel 
stokers. 

FULTON,  CHARLES  HERMAN.  Principles  of  Metallurgy.  New  York, 
McGraw-Hill  Co.,  1910,  p.  422-424. 

GEBHARDT,  G.  F.  Steam  Power  Plant  Engineering.  Ed.  4.  New  York, 
Wiley,  1913,  p.  58-66. 

GROVES,  CHARLES  EDWARD,  AND  THORP,  WILLIAM.  Chemical  Tech- 
nology, vol.  1.  Fuel  and  its  Applications.  By  E.  J.  Mills  and  F.  R. 
Rowan.  Philadelphia,  Blakiston,  1889,  p.  364,  664. 

HOFMAN,  H.  0.  General  Metallurgy.  New  Yorkf  McGraw-Hill  Book  Co., 
1913,  p.  183-189.  Mention  is  made  of  the  early  attempts  to  utilize 
coal  dust  as  fuel,  beginning  with  Niepce  in  1818.  A  list  of  refer- 
ences is  given. 

HUTTON,  FREDERICK  REMSEN.  The  Mechanical  Engineering  of  Steam 
Power  Plants.  Ed.  3.  New  York,  Wiky,  1908.  Chapter  9— Firing 
boilers  with  gas  or  liquid  hydrocarbon  or  with  pulverized  fuel. 

KENT,  WM.    Steam  Boiler  Economy.   New  York,  Wiley,  1901,  p.  132, 183. 


202  POWDERED  COAL  AS  A  FUEL 

PUETSCH,  ALBERT.  Gas  and  Coal  Dust  Firing:  a  critical  review  of  the 
various  appliances  patented  in  Germany  for  this  purpose  since 
1885;  translated  by  Charles  Salter.  London,  1901. 

THURSTON,  R.  H.  A  Manual  of  Steam  Boilers,  their  design,  construc- 
tion and  operation.  New  York,  Wiky,  1888,  p.  164-165.  Paragraph 
on  pulverized  coal. 

TURIN,  ANDRE.  Les  foyers  de  chaudi&res.  Pan's,  Dunod  &  Pinat, 
1913,  p.  156-161. 

U.  S.  STEAM  ENGINEERING  BUREAU  (NAVY  DEPARTMENT).  Annual 
Report,  1876.  Washington,  Govt.,  1876.  Experiments  were  made 
under  the  direction  of  B.  F.  Isherwood,  with  a  horizontal  fire-tube 
boiler,  at  East  Boston,  Mass.,  to  test  the  process  of  Whelpley  and 
Storer  for  effecting  the  combustion  of  coal  dust.  The  apparatus 
for  grinding  the  coal  was  the  only  part  of  the  process  which  was 
patented.  The  coal  dust  was  blown  upon  a  bed  of  ignited  lump 
coal.  Tables  are  given,  showing  the  comparative  economy  of  burn- 
ing lump  coal  alone,  or  lump  coal  with  coal  dust.  It  was  found  that 
the  use  of  powdered  fuel  was  more  expensive,  on  account  of  the 
cost  of  pulverization. 


INDEX 


Aero  pulverizer,  36 
Air-distributing  system,  58 

vs.  screw  conveyors,  59 
Air  separation,  32 

volumes  and  weights  of  dry  air  (tables),  33 
Air  separators,  32 

American  iron  and  steel  plants,  re  powdered  coal,  130 
American  Locomotive  Co.,  re  powdered  coal,  126 
Anaconda  plant,  re  powdered  coal,  96 
Analyses : 

B.t.u.  cost,  1 

coal  giving  good  results,  2,  12,  15 

comparison  of  fuel  oil  vs.  powdered  coal,  15 
Ash,  13 

disposal  of,  17 

elimination  from  furnaces,  61 

ferric  oxide  in,  14 

ferric  sulphide  in,  14 

ferrous  oxide  in,  14 

trouble  from,  17 

vs.  efficiency,  13,  14,  15 
Atlas  Portland  Cement  Co.,  re  powdered  coal,  62 

Bonnot  pulverizer,  37 
capacities  of,  41 
tube  mill,  40 

British  thermal  unit.    See  B.t.u.  cost. 
B.t.u.  cost: 
analysis  of,  1 

comparative  efficiencies  of  fuels,  1 
elementary  factor  in  choice  of  fuel,  1 
in  metallurgical  furnaces,  101 
summaries  of,  7 
Burners,  50,  51 
Busheling  furnaces,  105 

203 


204  INDEX 

Canadian  Copper  Co.,  re  powdered  coal,  84 
Cement: 

Atlas  Portland  Cement  Co.,  experiments  by,  62 

capacity  of  kilns,  73 

combustion  by  Edison  System,  68 
character  of,  in  cement  kilns,  66 

Edison  system  of  burning  clinker,  68 

economy  of  dry  vs.  wet  coal,  73 

flue  losses  in  rotary  kiln,  74 

heat  required  for  Portland  cement,  74 

kiln  calculations,  73 

material  required  for  Portland  cement,  74 

method  of  manufacture,  63 

oil  as  fuel  in  manufacture  of,  62 

powdered  coal  as  fuel  in  manufacture  of,  62 

rotary  cement  kiln,  64 

temperature  of  kiln  by  Edison  System,  71 

utilization  of  waste  heat  in  kiln,  75 
of  waste  heat  of  escaping  gases,  76 

See  Powdered  Coal. 
Clinker  and  slag,  16 

"hard  clinker,"  14 

"honeycomb"  (flue-sheet),  14,  15 

"soft  clinker,"  14 
Coal: 

analysis  of  those  giving  good  results,  2,  12 

anthracite  and  semi-bituminous  vs.  bituminous,  10 

crushed,  18,  19,  138 

high  vs.  low-grade,  8,  126 

price  of,  1 

raw  vs.  powdered,  1 

staple  fuel  of  metal-working  industries,  1 

suitable  for  powdering,  2,  8 

summary,  12 

See  Powdered  Coal. 
Combustion,  42,  45,  66,  68,  82 

See  Cement;  Powdered  Coal;  Temperature. 
Comparison  of  costs  of  powdered  coal  vs.  fuel-oil  and  gas,  3 
Cost,  B.t.u.: 

amount  of  coal  vs.  quality,  158 

analysis  of,  1 

an  elementary  factor  in  choice  of  fuels,  1 

comparative  efficiencies  of  fuels,  1 


INDEX  205 

Cost,  B.t.u. — Continued 
in  firing  under  boilers,  153 
in  metallurgical  furnaces,  101 
installation  of  dryers,  21 
of  fuel  in  metallurgical  furnaces,  99 
production  vs.  input,  operator,  output,  101 
to  operate  locomotives,  162 

See  Locomotives;  Metallurgical  Furnaces;  Powdered  Coal. 
Crushed  coal,  138 

crushers,  Jeffrey  Single-Roll,  18, 

"S-A,"  19 
crushing  coal,  18 

Ding  "magnetic  pulley,"  20 
Distribution  of  coal,  1 
Drying  coal: 

before  powdering,  20,  22 

dry  vs.  wet,  21 

Ruggles-Coles  dryer,  24 

theory  of,  22 

Early  use  of  powdered  coal,  163 
Edison  system,  68 
Efficiency: 

ash  vs.,  13 

clinker,  14 

comparative,  as  by  fuels,  1,  101 

determination  of,  101 

quality  of  ash  as  a  factor  of,  13 
Elimination  of  smoke,  136 
Explosions,  178 

coal,  178 

confusion  between  coal  and  dust,  178,  182 

grinding-room  dangers,  178,  182 

precautions  against,  188 

spontaneous  combustion,  184 

ways  of  safety,  184 

Ferric  oxide  in  ash,  14 
Ferric  sulphide  in  ash,  14 
Ferrous  oxide  in  ash,  14 
"Flue-sheet  clinker,"  14 


206  INDEX 

Fuel: 

coal  the  staple,  1 
vs.  efficiency,  101 
Furnaces  for  burning  powdered  coal,  49 

busheling  furnaces,  105 

heating  furnaces,  105 

metallurgical  furnaces,  99 

puddling  furnaces,  105 

reverberatory  furnaces,  78 

air-distributing  system,  58;  vs.  screw  conveyors,  59 
apparatus  for  proportioning  fuel  and  heat,  109,  110 
burners,  50 

changing  oil  furnaces  to  coal,  117 
comparison  of  forging  heats,  122 
construction  of,  117 

construction  for  use  under  boilers,  139,  159 
control  of  feed,  130 

cost  of  fuel  in  metal-working  furnaces,  99,  134 
delivering  powdered  coal  into,  107 
durability,  120 

Edison  patents  on  burning  and  feeding  equipment,  58 
elimination  of  ash  and  smoke,  61 
heats,  evenness  by  powdered  coal,  125 
maintenance  at  given  temperature,  122 
treatment  in  metal-working  furnaces,  99 
introduction  of  air  into,  51 

tubes,  52 
lining  of,  120,  121 
oil  vs.  powdered  coal,  130 
preparation  of  powdered  coal  for  use  in,  107 
repairs,  cost  of,  136 

screw  conveyors  vs.  air-distributing  system,  59 
tubes,  52 

See  Busheling  Furnaces;    Heating  Furnaces;    Metallurgical  Furnaces; 
Powdered  Coal;  Puddling  Furnaces;  Reverberatory  Furnaces. 

Gas,  efficiency  cost  vs.  powdered  coal,  1 

Gases,  utilization  of  waste  heat  escaping  from,  76 

General  Electric  Co.,  re  metallurgical  furnaces  and  powdered  coal,  111 

Grinding  ring,  29 

"Hard  clinker,"  14 

Heating  furnaces.  105,  133,  134 


INDEX  207 

Heat  treatment  in  metallurgical  furnaces,  99 
Heat,  utilization  of  waste,  75 
Holbeck  air-distributing  system,  58 
"Honeycomb  clinker,"  15 

Input,  101 

Iron  pyrites  in  ash,  14 

Jeffrey  Single-roll  crusher,  18 

Kiln: 

calculations,  73 
capacity,  73 
See  Cement. 

Locomotives,  run  by  powdered  coal: 

elimination  of  smoke,  soot,  waste  products,  161,  162 

equipment  for  using  powdered  coal,  65 

maintenance  of  fire-box  temperature,  162 

operation  with  powdered  coal,  169 

performance,  173 

reduction  in  maintenance  and  operating  costs,  162 

saving  in  coal,  162 

successful  installations,  164 

sustained  boiler  capacity,  162 

See  Powdered  Coal. 

Magnetic  pulley,  Ding,  20 
Magnetic  separator,  20 

i 

Oil,  fuel: 

efficiency  cost  vs.  powdered  coal,  1 

in  the  cement  industry,  62 

in  metallurgical  furnaces,  99 
Open-hearth  work,  105,  132 

Operation  of  furnaces  and  plants  with  powdered  coal,  2,  169 
Operator  a  great  factor  in  successful  running  of  furnaces,  101 
Output,  101 
Oxide,  ferric,  in  ash,  14 
ferrous,  in  ash,  14 

Plants  using  powdered  coal; 

cost,  first,  of  installation  of  fuel  oil,  3 


208  INDEX 

Plants  using  powdered  coal — Continued 
cost  of  gas,  4 

of  powdered  coal,  with  screw  conveyors,  5 
of    powdered     coal,     with    pneumatic    air-distributing    sys- 
tem, 7 

cost  of  operation  with  fuel  oil,  6 
with  gas,  6 

with  powdered  coal,  screw  conveyors,  6 
with  powdered  coal,  air-distributing  system,  7 
summaries,  7 

Pneumatic  distribution,  7,  51 
Pneumatic  feeding  system,  58 
Powdered  coal  as  a  fuel,  1 

air  separation,  32 

analyses,  1,  2,  12,  15 

anthracite  vs.  semi-bituminous  vs.  bituminous,  10 

apparatus,  91,  93 

arrangement  of  air  piping,  133 

as  fuel,  43 

ash  question,  13 

Bettington  boiler,  144 

Blake  apparatus,  142 

Bonnot  pulverizer,   37;    tube  mill,  40;    capacities  of  tube 

mills,  41 

busheling  furnaces,  105 
care  by  operators,  45 
cement  industry,  62 
class  of  coal  for  pulverization,  2,  8 
coal  suitable  for  powdering,  8 
combustion,  42,  82;   difference  in  results  from  powdered  and 

raw,  44 

comparison  of  costs  of  fuel-oil,  gas  and  powdered  coal,  45 
construction  of  furnaces  for  use  under  boilers,  139 
cost,  first,  of  plant  for  fuel  oil,  3 
for  gas,  4 

for  powdered  coal,  screw  conveyors,  5 
for  powdered  coal,  air-distributing  system,  5 
cost  of  operating  plant  with  fuel  oil,  6 
with  gas,  6 

with  powdered  coal,  screw  conveyors,  6 
with  powdered  coal,  air-distributing  system,  7 
summaries,  7 
See  Cement;  Coal;  Furnaces. 


INDEX  209 

Powdered  coal  as  a  fuel — Continued 

cost  on  firing  under  boilers,  153 

cost  of  labor  and  maintenance  with  Raymond  crusher,  18 

Day  or  ideal  apparatus,  142 

delivery  to  furnace,  132 

difficulties  in  operating,  81 

circumvention  of  these,  81 
Ding  "magnetic  pulley,"  20 
dry  vs.  wet  coal  for  powdering,  21,  73 
drying,  20,  22 

experiments  by  the  Atlas  Portland  Cement  Co.,  62 
explosions,  188.    See  Explosions, 
feeding  and  burning,  42 
fuel-oil  and  gas  vs.  powdered  coal,  1 
fuel  ratio  and  furnace  practice  in  smelting,  83 
furnaces  for  powdered  coal,  49,  139 
General  Electric  Co.,  boiler,  147 
grinding  ring,  29 
heating  furnaces,  105 
high  vs.  low-grade  coal,  8 
Holbeck  system,  5 
indirect-fired  rotary  dryer,  23 
Jeffrey  pulverizer,  35 
Jeffrey  single-roll  crusher,  18 
locomotives  run  by,  161 

cost  of  reduction  of  maintenance  and  operation,  162 

elimination  of  smoke,  soot,  waste  products,  161,  162 

equipment,  165 

performance,  173 

maintenance  of  boiler  capacities  and  fire-box  temperatures, 
162 

operation,  169 

saving  in  coal,  162 

successful  installations,  164 

sustained  boiler  capacities,  162 
metallurgical  furnaces,  99 

as  used  by  American  iron  and  steel  plants,  130 

by  American  Locomotive  Co.,  126 

by  General  Electric  Co.,  Ill 

B.t.u.,  101 

cost  of  fuel  vs.  output,  99 

determination  of  efficiency,  101 

efficiency  vs.  fuel,  101 


INDEX 

Powdered  coal  as  a  fuel — Continued 

metallurgical  furnaces,  factors  contributing  to  profitable  use 

104 

gas  vs.  powdered  coal,  99 
heat  treatment,  99 
laws  of  thermo-chemistry  anent  oxygen  vs.  temperature, 

102 

maintenance  of  heats  at  will,  122 
moisture,  132 
operator,  101 
production  costs  dependent  upon  input,  operator,  output, 

101 

temperatures  in  metal  work,  103. 
See  Metallurgical  Furnaces, 
oil  vs.  powdered  coal  furnaces,  130 
open-hearth  work,  105 
operation,  of  plant,  2 
Pinther  apparatus,  2 
plants  using,  2 

preparation  for  and  delivering  into  furnaces,  18,  107,  132 
puddling  furnaces,  105 
pulverization,  132 
pulverizer  mill,  27 
aero  pulverizer,  36 

Raymond  Bros/  impact  pulverizer,  30 
table  of  pulverizers,  34 
raw  vs.  powdered  coal,  44 
reverberatory  furnaces,  78 

economical  in  use,  78 
Ruggles-Coles  dryer,  24 
Schwartzkopf  apparatus,  142 
smelting  (new),  process,  80,  93,  96 
summary,  12 

temperatures  attained  in  combustion,  45 
tendency  to  clog  and  pack,  116 
volumes  and  weights  of  dry  air,  33 
See  Coal;  Furnaces;  Locomotives. 
Preparation  of  powdered  coal,  18 
Price  of  coal,  1 

Puddling  furnaces,  105,  132,  133,  134 
Pulley,  Ding  magnetic,  20 
Pulverizers,  27,  30,  34,  35,  36,  37 
Pyrites,  iron,  in  ash,  14 


INDEX  211 

Raw  coal,  efficiency  cost  us.  powdered  coal,  1 
Repairs  on  furnaces,  136 

Screw  conveyors  vs.  air-distributing  system,  59 
Separation,  air,  32 

volumes  and  weights  of  dry  air,  33 
Separator,  magnetic,  20 
Slag  and  clinker,  16 
Smoke,  elimination  of,  61,  136 
"Soft  clinker,"  14 
Storage  difficulties,  188 
Summaries,   installation  and  operating    costs  of  plants  using  fuel-oil 

gas,  powdered  coal,  7 

Temperatures: 

attained  by  combustion  of  powdered  coal,  45 

in  cement  kilns  by  Edison  System,  71 

maintenance  at  given  amount  by  use  of  powdered  coal,  122 

oxygen  vs.  laws  anent,  102 

in  metal  work,  103 
Tube  mills,  Bonnot,  41 

Utilization  of  waste  heat,  75,  76 

Volumes  and  weights  of  dry  air  (tables),  33 

Washoe  Reduction  Works,  re  powdered  coal,  93 
Waste  heat: 

utilization  in  cement  manufacture,  75 

utilization  of  that  from  escaping  gases,  76 
Weights  and  volumes  of  dry  air  (tables),  33 


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